thr3ads.net - Virtualization - [PATCH 1/3] x86/xen: Avoid fast syscall path for Xen PV guests [Nov 2015]

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Boris Ostrovsky

2015-Nov-18 20:06 UTC

[PATCH 0/3] Fix and cleanup for 32-bit PV sysexit

The first patch fixes Xen PV regression introduced by 32-bit rewrite. Unlike the
earlier version it uses ALTERNATIVE instruction and avoids using xen_sysexit
(and sysret32 in compat mode) pv ops, as suggested by Andy. (I ended up patching
TEST with XOR to avoid extra NOPs, even though I said yesterday it would be
wrong. It's not wrong)

As result of this patch irq_enable_sysexit and usergs_sysret32 pv ops are not
used anymore by anyone and so can be removed.

Boris Ostrovsky (3):
  x86/xen: Avoid fast syscall path for Xen PV guests
  x86: irq_enable_sysexit pv op is no longer needed
  x86: usergs_sysret32 pv op is no longer needed

 arch/x86/entry/entry_32.S             | 11 ++++-------
 arch/x86/entry/entry_64_compat.S      | 16 ++++++----------
 arch/x86/include/asm/cpufeature.h     |  1 +
 arch/x86/include/asm/paravirt.h       | 12 ------------
 arch/x86/include/asm/paravirt_types.h | 17 -----------------
 arch/x86/kernel/asm-offsets.c         |  3 ---
 arch/x86/kernel/asm-offsets_64.c      |  1 -
 arch/x86/kernel/paravirt.c            | 12 ------------
 arch/x86/kernel/paravirt_patch_32.c   |  2 --
 arch/x86/kernel/paravirt_patch_64.c   |  3 ---
 arch/x86/xen/enlighten.c              |  7 +++----
 arch/x86/xen/xen-asm_32.S             | 14 --------------
 arch/x86/xen/xen-asm_64.S             | 19 -------------------
 arch/x86/xen/xen-ops.h                |  3 ---
 14 files changed, 14 insertions(+), 107 deletions(-)

-- 
1.8.1.4

Boris Ostrovsky

2015-Nov-18 20:06 UTC

head link

[PATCH 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
("x86/entry/32: Re-implement SYSENTER using the new C path"), the
stack
frame that is passed to xen_sysexit is no longer a "standard" one
(i.e.
it's not pt_regs).

Since we end up calling xen_iret from xen_sysexit we don't need to fix
up the stack and instead follow entry_SYSENTER_32's IRET path directly
to xen_iret.

We can do the same thing for compat mode even though stack does not need
to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in
the subsequent patch)

Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Suggested-by: Andy Lutomirski <luto at amacapital.net>
---
 arch/x86/entry/entry_32.S         | 3 ++-
 arch/x86/entry/entry_64_compat.S  | 6 ++++--
 arch/x86/include/asm/cpufeature.h | 1 +
 arch/x86/xen/enlighten.c          | 4 +++-
 4 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3eb572e..901f186 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -308,7 +308,8 @@ sysenter_past_esp:
 
 	movl	%esp, %eax
 	call	do_fast_syscall_32
-	testl	%eax, %eax
+	/* XEN PV guests always use IRET path */
+	ALTERNATIVE "testl %eax, %eax", "xor %eax, %eax",
X86_FEATURE_XENPV
 	jz	.Lsyscall_32_done
 
 /* Opportunistic SYSEXIT */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c320183..98893d9 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -121,7 +121,8 @@ sysenter_flags_fixed:
 
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
-	testl	%eax, %eax
+	/* XEN PV guests always use IRET path */
+	ALTERNATIVE "testl %eax, %eax", "xor %eax, %eax",
X86_FEATURE_XENPV
 	jz	.Lsyscall_32_done
 	jmp	sysret32_from_system_call
 
@@ -200,7 +201,8 @@ ENTRY(entry_SYSCALL_compat)
 
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
-	testl	%eax, %eax
+	/* XEN PV guests always use IRET path */
+	ALTERNATIVE "testl %eax, %eax", "xor %eax, %eax",
X86_FEATURE_XENPV
 	jz	.Lsyscall_32_done
 
 	/* Opportunistic SYSRET */
diff --git a/arch/x86/include/asm/cpufeature.h
b/arch/x86/include/asm/cpufeature.h
index e4f8010..0e4fe5b 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -216,6 +216,7 @@
 #define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
 #define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
 #define X86_FEATURE_VMMCALL     ( 8*32+15) /* Prefer vmmcall to vmcall */
+#define X86_FEATURE_XENPV       ( 8*32+16) /* Xen paravirtual guest */
 
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5774800..d315151 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
 static void xen_set_cpu_features(struct cpuinfo_x86 *c)
 {
-	if (xen_pv_domain())
+	if (xen_pv_domain()) {
 		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+		set_cpu_cap(c, X86_FEATURE_XENPV);
+	}
 }
 
 const struct hypervisor_x86 x86_hyper_xen = {
-- 
1.8.1.4

Boris Ostrovsky

2015-Nov-18 20:06 UTC

head link

[PATCH 2/3] x86: irq_enable_sysexit pv op is no longer needed

Xen PV guests have been the only ones using it and now they don't.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
---
 arch/x86/entry/entry_32.S             |  8 ++------
 arch/x86/include/asm/paravirt.h       |  7 -------
 arch/x86/include/asm/paravirt_types.h |  9 ---------
 arch/x86/kernel/asm-offsets.c         |  3 ---
 arch/x86/kernel/paravirt.c            |  7 -------
 arch/x86/kernel/paravirt_patch_32.c   |  2 --
 arch/x86/kernel/paravirt_patch_64.c   |  1 -
 arch/x86/xen/enlighten.c              |  3 ---
 arch/x86/xen/xen-asm_32.S             | 14 --------------
 arch/x86/xen/xen-ops.h                |  3 ---
 10 files changed, 2 insertions(+), 55 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 901f186..e2158ae 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -329,7 +329,8 @@ sysenter_past_esp:
 	 * Return back to the vDSO, which will pop ecx and edx.
 	 * Don't bother with DS and ES (they already contain __USER_DS).
 	 */
-	ENABLE_INTERRUPTS_SYSEXIT
+	sti
+	sysexit
 
 .pushsection .fixup, "ax"
 2:	movl	$0, PT_FS(%esp)
@@ -552,11 +553,6 @@ ENTRY(native_iret)
 	iret
 	_ASM_EXTABLE(native_iret, iret_exc)
 END(native_iret)
-
-ENTRY(native_irq_enable_sysexit)
-	sti
-	sysexit
-END(native_irq_enable_sysexit)
 #endif
 
 ENTRY(overflow)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 10d0596..c28518e 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -932,13 +932,6 @@ extern void default_banner(void);
 	push %ecx; push %edx;				\
 	call PARA_INDIRECT(pv_cpu_ops+PV_CPU_read_cr0);	\
 	pop %edx; pop %ecx
-
-#define ENABLE_INTERRUPTS_SYSEXIT					\
-	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_irq_enable_sysexit),	\
-		  CLBR_NONE,						\
-		  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_irq_enable_sysexit))
-
-
 #else	/* !CONFIG_X86_32 */
 
 /*
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 31247b5..608bbf3 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -157,15 +157,6 @@ struct pv_cpu_ops {
 
 	u64 (*read_pmc)(int counter);
 
-#ifdef CONFIG_X86_32
-	/*
-	 * Atomically enable interrupts and return to userspace.  This
-	 * is only used in 32-bit kernels.  64-bit kernels use
-	 * usergs_sysret32 instead.
-	 */
-	void (*irq_enable_sysexit)(void);
-#endif
-
 	/*
 	 * Switch to usermode gs and return to 64-bit usermode using
 	 * sysret.  Only used in 64-bit kernels to return to 64-bit
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 439df97..84a7524 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -65,9 +65,6 @@ void common(void) {
 	OFFSET(PV_IRQ_irq_disable, pv_irq_ops, irq_disable);
 	OFFSET(PV_IRQ_irq_enable, pv_irq_ops, irq_enable);
 	OFFSET(PV_CPU_iret, pv_cpu_ops, iret);
-#ifdef CONFIG_X86_32
-	OFFSET(PV_CPU_irq_enable_sysexit, pv_cpu_ops, irq_enable_sysexit);
-#endif
 	OFFSET(PV_CPU_read_cr0, pv_cpu_ops, read_cr0);
 	OFFSET(PV_MMU_read_cr2, pv_mmu_ops, read_cr2);
 #endif
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index c2130ae..c55f437 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -162,9 +162,6 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void
*insnbuf,
 		ret = paravirt_patch_ident_64(insnbuf, len);
 
 	else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||
-#ifdef CONFIG_X86_32
-		 type == PARAVIRT_PATCH(pv_cpu_ops.irq_enable_sysexit) ||
-#endif
 		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
 		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret64))
 		/* If operation requires a jmp, then jmp */
@@ -220,7 +217,6 @@ static u64 native_steal_clock(int cpu)
 
 /* These are in entry.S */
 extern void native_iret(void);
-extern void native_irq_enable_sysexit(void);
 extern void native_usergs_sysret32(void);
 extern void native_usergs_sysret64(void);
 
@@ -379,9 +375,6 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 
 	.load_sp0 = native_load_sp0,
 
-#if defined(CONFIG_X86_32)
-	.irq_enable_sysexit = native_irq_enable_sysexit,
-#endif
 #ifdef CONFIG_X86_64
 #ifdef CONFIG_IA32_EMULATION
 	.usergs_sysret32 = native_usergs_sysret32,
diff --git a/arch/x86/kernel/paravirt_patch_32.c
b/arch/x86/kernel/paravirt_patch_32.c
index c89f50a..158dc06 100644
--- a/arch/x86/kernel/paravirt_patch_32.c
+++ b/arch/x86/kernel/paravirt_patch_32.c
@@ -5,7 +5,6 @@ DEF_NATIVE(pv_irq_ops, irq_enable, "sti");
 DEF_NATIVE(pv_irq_ops, restore_fl, "push %eax; popf");
 DEF_NATIVE(pv_irq_ops, save_fl, "pushf; pop %eax");
 DEF_NATIVE(pv_cpu_ops, iret, "iret");
-DEF_NATIVE(pv_cpu_ops, irq_enable_sysexit, "sti; sysexit");
 DEF_NATIVE(pv_mmu_ops, read_cr2, "mov %cr2, %eax");
 DEF_NATIVE(pv_mmu_ops, write_cr3, "mov %eax, %cr3");
 DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %cr3, %eax");
@@ -46,7 +45,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
 		PATCH_SITE(pv_irq_ops, restore_fl);
 		PATCH_SITE(pv_irq_ops, save_fl);
 		PATCH_SITE(pv_cpu_ops, iret);
-		PATCH_SITE(pv_cpu_ops, irq_enable_sysexit);
 		PATCH_SITE(pv_mmu_ops, read_cr2);
 		PATCH_SITE(pv_mmu_ops, read_cr3);
 		PATCH_SITE(pv_mmu_ops, write_cr3);
diff --git a/arch/x86/kernel/paravirt_patch_64.c
b/arch/x86/kernel/paravirt_patch_64.c
index 8aa0558..17c00f8 100644
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -13,7 +13,6 @@ DEF_NATIVE(pv_mmu_ops, flush_tlb_single, "invlpg
(%rdi)");
 DEF_NATIVE(pv_cpu_ops, clts, "clts");
 DEF_NATIVE(pv_cpu_ops, wbinvd, "wbinvd");
 
-DEF_NATIVE(pv_cpu_ops, irq_enable_sysexit, "swapgs; sti; sysexit");
 DEF_NATIVE(pv_cpu_ops, usergs_sysret64, "swapgs; sysretq");
 DEF_NATIVE(pv_cpu_ops, usergs_sysret32, "swapgs; sysretl");
 DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index d315151..a068e36 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1229,10 +1229,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst =
{
 
 	.iret = xen_iret,
 #ifdef CONFIG_X86_64
-	.usergs_sysret32 = xen_sysret32,
 	.usergs_sysret64 = xen_sysret64,
-#else
-	.irq_enable_sysexit = xen_sysexit,
 #endif
 
 	.load_tr_desc = paravirt_nop,
diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
index fd92a64..feb6d40 100644
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -35,20 +35,6 @@ check_events:
 	ret
 
 /*
- * We can't use sysexit directly, because we're not running in ring0.
- * But we can easily fake it up using iret.  Assuming xen_sysexit is
- * jumped to with a standard stack frame, we can just strip it back to
- * a standard iret frame and use iret.
- */
-ENTRY(xen_sysexit)
-	movl PT_EAX(%esp), %eax			/* Shouldn't be necessary? */
-	orl $X86_EFLAGS_IF, PT_EFLAGS(%esp)
-	lea PT_EIP(%esp), %esp
-
-	jmp xen_iret
-ENDPROC(xen_sysexit)
-
-/*
  * This is run where a normal iret would be run, with the same stack setup:
  *	8: eflags
  *	4: cs
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 1399423..4140b07 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -139,9 +139,6 @@ DECL_ASM(void, xen_restore_fl_direct, unsigned long);
 
 /* These are not functions, and cannot be called normally */
 __visible void xen_iret(void);
-#ifdef CONFIG_X86_32
-__visible void xen_sysexit(void);
-#endif
 __visible void xen_sysret32(void);
 __visible void xen_sysret64(void);
 __visible void xen_adjust_exception_frame(void);
-- 
1.8.1.4

Boris Ostrovsky

2015-Nov-18 20:06 UTC

head link

[PATCH 3/3] x86: usergs_sysret32 pv op is no longer needed

Xen PV guests have been the only ones using it and now they don't.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
---
 arch/x86/entry/entry_64_compat.S      | 10 ++--------
 arch/x86/include/asm/paravirt.h       |  5 -----
 arch/x86/include/asm/paravirt_types.h |  8 --------
 arch/x86/kernel/asm-offsets_64.c      |  1 -
 arch/x86/kernel/paravirt.c            |  5 -----
 arch/x86/kernel/paravirt_patch_64.c   |  2 --
 arch/x86/xen/xen-asm_64.S             | 19 -------------------
 7 files changed, 2 insertions(+), 48 deletions(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 98893d9..82415dc 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -18,13 +18,6 @@
 
 	.section .entry.text, "ax"
 
-#ifdef CONFIG_PARAVIRT
-ENTRY(native_usergs_sysret32)
-	swapgs
-	sysretl
-ENDPROC(native_usergs_sysret32)
-#endif
-
 /*
  * 32-bit SYSENTER instruction entry.
  *
@@ -238,7 +231,8 @@ sysret32_from_system_call:
 	xorq	%r9, %r9
 	xorq	%r10, %r10
 	movq	RSP-ORIG_RAX(%rsp), %rsp
-        USERGS_SYSRET32
+	swapgs
+	sysretl
 END(entry_SYSCALL_compat)
 
 /*
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index c28518e..1b71c3a 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -922,11 +922,6 @@ extern void default_banner(void);
 		  call PARA_INDIRECT(pv_irq_ops+PV_IRQ_irq_enable);	\
 		  PV_RESTORE_REGS(clobbers | CLBR_CALLEE_SAVE);)
 
-#define USERGS_SYSRET32							\
-	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret32),	\
-		  CLBR_NONE,						\
-		  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret32))
-
 #ifdef CONFIG_X86_32
 #define GET_CR0_INTO_EAX				\
 	push %ecx; push %edx;				\
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 608bbf3..702c8bd 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -165,14 +165,6 @@ struct pv_cpu_ops {
 	 */
 	void (*usergs_sysret64)(void);
 
-	/*
-	 * Switch to usermode gs and return to 32-bit usermode using
-	 * sysret.  Used to return to 32-on-64 compat processes.
-	 * Other usermode register state, including %esp, must already
-	 * be restored.
-	 */
-	void (*usergs_sysret32)(void);
-
 	/* Normal iret.  Jump to this with the standard iret stack
 	   frame set up. */
 	void (*iret)(void);
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index d8f42f9..f2edafb 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -23,7 +23,6 @@ int main(void)
 {
 #ifdef CONFIG_PARAVIRT
 	OFFSET(PV_IRQ_adjust_exception_frame, pv_irq_ops, adjust_exception_frame);
-	OFFSET(PV_CPU_usergs_sysret32, pv_cpu_ops, usergs_sysret32);
 	OFFSET(PV_CPU_usergs_sysret64, pv_cpu_ops, usergs_sysret64);
 	OFFSET(PV_CPU_swapgs, pv_cpu_ops, swapgs);
 	BLANK();
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index c55f437..8c19b4d 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -162,7 +162,6 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void
*insnbuf,
 		ret = paravirt_patch_ident_64(insnbuf, len);
 
 	else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||
-		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
 		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret64))
 		/* If operation requires a jmp, then jmp */
 		ret = paravirt_patch_jmp(insnbuf, opfunc, addr, len);
@@ -217,7 +216,6 @@ static u64 native_steal_clock(int cpu)
 
 /* These are in entry.S */
 extern void native_iret(void);
-extern void native_usergs_sysret32(void);
 extern void native_usergs_sysret64(void);
 
 static struct resource reserve_ioports = {
@@ -376,9 +374,6 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.load_sp0 = native_load_sp0,
 
 #ifdef CONFIG_X86_64
-#ifdef CONFIG_IA32_EMULATION
-	.usergs_sysret32 = native_usergs_sysret32,
-#endif
 	.usergs_sysret64 = native_usergs_sysret64,
 #endif
 	.iret = native_iret,
diff --git a/arch/x86/kernel/paravirt_patch_64.c
b/arch/x86/kernel/paravirt_patch_64.c
index 17c00f8..e70087a 100644
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -14,7 +14,6 @@ DEF_NATIVE(pv_cpu_ops, clts, "clts");
 DEF_NATIVE(pv_cpu_ops, wbinvd, "wbinvd");
 
 DEF_NATIVE(pv_cpu_ops, usergs_sysret64, "swapgs; sysretq");
-DEF_NATIVE(pv_cpu_ops, usergs_sysret32, "swapgs; sysretl");
 DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");
 
 DEF_NATIVE(, mov32, "mov %edi, %eax");
@@ -54,7 +53,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
 		PATCH_SITE(pv_irq_ops, save_fl);
 		PATCH_SITE(pv_irq_ops, irq_enable);
 		PATCH_SITE(pv_irq_ops, irq_disable);
-		PATCH_SITE(pv_cpu_ops, usergs_sysret32);
 		PATCH_SITE(pv_cpu_ops, usergs_sysret64);
 		PATCH_SITE(pv_cpu_ops, swapgs);
 		PATCH_SITE(pv_mmu_ops, read_cr2);
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index f22667a..cc8acc4 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -68,25 +68,6 @@ ENTRY(xen_sysret64)
 ENDPATCH(xen_sysret64)
 RELOC(xen_sysret64, 1b+1)
 
-ENTRY(xen_sysret32)
-	/*
-	 * We're already on the usermode stack at this point, but
-	 * still with the kernel gs, so we can easily switch back
-	 */
-	movq %rsp, PER_CPU_VAR(rsp_scratch)
-	movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
-
-	pushq $__USER32_DS
-	pushq PER_CPU_VAR(rsp_scratch)
-	pushq %r11
-	pushq $__USER32_CS
-	pushq %rcx
-
-	pushq $0
-1:	jmp hypercall_iret
-ENDPATCH(xen_sysret32)
-RELOC(xen_sysret32, 1b+1)
-
 /*
  * Xen handles syscall callbacks much like ordinary exceptions, which
  * means we have:
-- 
1.8.1.4

Andy Lutomirski

2015-Nov-18 20:21 UTC

head link

[PATCH 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

On Wed, Nov 18, 2015 at 12:06 PM, Boris Ostrovsky
<boris.ostrovsky at oracle.com> wrote:> After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
> ("x86/entry/32: Re-implement SYSENTER using the new C path"), the
stack
> frame that is passed to xen_sysexit is no longer a "standard" one
(i.e.
> it's not pt_regs).
>
> Since we end up calling xen_iret from xen_sysexit we don't need to fix
> up the stack and instead follow entry_SYSENTER_32's IRET path directly
> to xen_iret.
>
> We can do the same thing for compat mode even though stack does not need
> to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in
> the subsequent patch)
Looks generally quite nice.  Minor comments below:
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -308,7 +308,8 @@ sysenter_past_esp:
>
>         movl    %esp, %eax
>         call    do_fast_syscall_32
> -       testl   %eax, %eax
> +       /* XEN PV guests always use IRET path */
> +       ALTERNATIVE "testl %eax, %eax", "xor %eax,
%eax", X86_FEATURE_XENPV
>         jz      .Lsyscall_32_done
Could we make this a little less subtle:

ALTERNATIVE "testl %eax, %eax; lz .Lsyscall_32_done", "jmp
.Lsyscasll_32_done", X86_FEATURE_XENPV

Borislav, what do you think?

Ditto for the others.
> diff --git a/arch/x86/include/asm/cpufeature.h
b/arch/x86/include/asm/cpufeature.h
> index e4f8010..0e4fe5b 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -216,6 +216,7 @@
>  #define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept
*/
>  #define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold
*/
>  #define X86_FEATURE_VMMCALL     ( 8*32+15) /* Prefer vmmcall to vmcall */
> +#define X86_FEATURE_XENPV       ( 8*32+16) /* Xen paravirtual guest */
>
This bit is highly magical and I think we need Borislav's ack.

--Andy

Andy Lutomirski

2015-Nov-18 20:23 UTC

head link

[PATCH 2/3] x86: irq_enable_sysexit pv op is no longer needed

On Wed, Nov 18, 2015 at 12:06 PM, Boris Ostrovsky
<boris.ostrovsky at oracle.com> wrote:> Xen PV guests have been the only ones using it and now they don't.
Fantastic!

--Andy

Andy Lutomirski

2015-Nov-18 20:26 UTC

head link

[PATCH 3/3] x86: usergs_sysret32 pv op is no longer needed

On Wed, Nov 18, 2015 at 12:06 PM, Boris Ostrovsky
<boris.ostrovsky at oracle.com> wrote:> Xen PV guests have been the only ones using it and now they don't.
Yay!

--Andy

Boris Ostrovsky

2015-Nov-18 20:34 UTC

head link

[PATCH 2/3] x86: irq_enable_sysexit pv op is no longer needed

On 11/18/2015 03:11 PM, Konrad Rzeszutek Wilk wrote:> On Wed, Nov 18, 2015 at 03:06:18PM -0500, Boris Ostrovsky wrote:
>> Xen PV guests have been the only ones using it and now they don't.
> Could you elaborate on the 'now they don't' please?
>
> Is Xen not doing it? Did it do it in the past?
>
> Is it because the Linux code paths will never run to this in Xen PV mode?
> Is that due to other patches? If so please mention the name
> of the other patches.. (so if somebody is thinking to put the
> other patches on the stable train they should also take these ones).
Since this is due to the first patch in the series I don't know its 
commitID. Should I just refer to patch title?

-boris

Borislav Petkov

2015-Nov-19 12:10 UTC

head link

[PATCH 0/3] Fix and cleanup for 32-bit PV sysexit

On Wed, Nov 18, 2015 at 03:06:16PM -0500, Boris Ostrovsky
wrote:> The first patch fixes Xen PV regression introduced by 32-bit rewrite.
Unlike the
> earlier version it uses ALTERNATIVE instruction and avoids using
xen_sysexit
> (and sysret32 in compat mode) pv ops, as suggested by Andy. (I ended up
patching
> TEST with XOR to avoid extra NOPs, even though I said yesterday it would be
> wrong. It's not wrong)
> 
> As result of this patch irq_enable_sysexit and usergs_sysret32 pv ops are
not
> used anymore by anyone and so can be removed.
> 
> Boris Ostrovsky (3):
>   x86/xen: Avoid fast syscall path for Xen PV guests
>   x86: irq_enable_sysexit pv op is no longer needed
>   x86: usergs_sysret32 pv op is no longer needed
> 
>  arch/x86/entry/entry_32.S             | 11 ++++-------
>  arch/x86/entry/entry_64_compat.S      | 16 ++++++----------
>  arch/x86/include/asm/cpufeature.h     |  1 +
>  arch/x86/include/asm/paravirt.h       | 12 ------------
>  arch/x86/include/asm/paravirt_types.h | 17 -----------------
>  arch/x86/kernel/asm-offsets.c         |  3 ---
>  arch/x86/kernel/asm-offsets_64.c      |  1 -
>  arch/x86/kernel/paravirt.c            | 12 ------------
>  arch/x86/kernel/paravirt_patch_32.c   |  2 --
>  arch/x86/kernel/paravirt_patch_64.c   |  3 ---
>  arch/x86/xen/enlighten.c              |  7 +++----
>  arch/x86/xen/xen-asm_32.S             | 14 --------------
>  arch/x86/xen/xen-asm_64.S             | 19 -------------------
>  arch/x86/xen/xen-ops.h                |  3 ---
>  14 files changed, 14 insertions(+), 107 deletions(-)
Can't argue with that diffstat!

:-)

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imend?rffer, Jane Smithard, Graham Norton, HRB 21284
(AG N?rnberg)
--

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