The long term plan has been to replace Xen PV guests by PVH. The first victim of that plan are now 32-bit PV guests, as those are used only rather seldom these days. Xen on x86 requires 64-bit support and with Grub2 now supporting PVH officially since version 2.04 there is no need to keep 32-bit PV guest support alive in the Linux kernel. Additionally Meltdown mitigation is not available in the kernel running as 32-bit PV guest, so dropping this mode makes sense from security point of view, too. Juergen Gross (2): x86/xen: remove 32-bit Xen PV guest support x86/paravirt: remove 32-bit support from PARAVIRT_XXL arch/x86/entry/entry_32.S | 93 -------- arch/x86/entry/vdso/vdso32/vclock_gettime.c | 1 + arch/x86/include/asm/paravirt.h | 105 +-------- arch/x86/include/asm/paravirt_types.h | 20 -- arch/x86/include/asm/pgtable-3level_types.h | 5 - arch/x86/include/asm/proto.h | 2 +- arch/x86/include/asm/segment.h | 2 +- arch/x86/include/asm/traps.h | 2 +- arch/x86/kernel/cpu/common.c | 8 - arch/x86/kernel/paravirt.c | 17 -- arch/x86/kernel/paravirt_patch_32.c | 36 +-- arch/x86/xen/Kconfig | 3 +- arch/x86/xen/Makefile | 4 +- arch/x86/xen/apic.c | 17 -- arch/x86/xen/enlighten_pv.c | 45 +--- arch/x86/xen/mmu_pv.c | 326 +++------------------------- arch/x86/xen/p2m.c | 4 - arch/x86/xen/setup.c | 44 +--- arch/x86/xen/smp_pv.c | 19 +- arch/x86/xen/xen-asm.S | 14 -- arch/x86/xen/xen-asm_32.S | 207 ------------------ arch/x86/xen/xen-head.S | 6 - arch/x86/xen/xen-ops.h | 5 - drivers/xen/Kconfig | 4 +- 24 files changed, 57 insertions(+), 932 deletions(-) delete mode 100644 arch/x86/xen/xen-asm_32.S -- 2.16.4
Juergen Gross
2019-Jul-15 11:37 UTC
[PATCH 2/2] x86/paravirt: remove 32-bit support from PARAVIRT_XXL
The last 32-bit user of stuff under CONFIG_PARAVIRT_XXL is gone.
Remove 32-bit specific parts.
Signed-off-by: Juergen Gross <jgross at suse.com>
---
arch/x86/entry/vdso/vdso32/vclock_gettime.c | 1 +
arch/x86/include/asm/paravirt.h | 105 ++++------------------------
arch/x86/include/asm/paravirt_types.h | 20 ------
arch/x86/include/asm/pgtable-3level_types.h | 5 --
arch/x86/kernel/cpu/common.c | 8 ---
arch/x86/kernel/paravirt.c | 17 -----
arch/x86/kernel/paravirt_patch_32.c | 36 +---------
7 files changed, 15 insertions(+), 177 deletions(-)
diff --git a/arch/x86/entry/vdso/vdso32/vclock_gettime.c
b/arch/x86/entry/vdso/vdso32/vclock_gettime.c
index 9242b28418d5..36f4ce1405cb 100644
--- a/arch/x86/entry/vdso/vdso32/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vdso32/vclock_gettime.c
@@ -17,6 +17,7 @@
#undef CONFIG_ILLEGAL_POINTER_VALUE
#undef CONFIG_SPARSEMEM_VMEMMAP
#undef CONFIG_NR_CPUS
+#undef CONFIG_PARAVIRT_XXL
#define CONFIG_X86_32 1
#define CONFIG_PGTABLE_LEVELS 2
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index c25c38a05c1c..60dfa93313a9 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -139,7 +139,6 @@ static inline void __write_cr4(unsigned long x)
PVOP_VCALL1(cpu.write_cr4, x);
}
-#ifdef CONFIG_X86_64
static inline unsigned long read_cr8(void)
{
return PVOP_CALL0(unsigned long, cpu.read_cr8);
@@ -149,7 +148,6 @@ static inline void write_cr8(unsigned long x)
{
PVOP_VCALL1(cpu.write_cr8, x);
}
-#endif
static inline void arch_safe_halt(void)
{
@@ -283,12 +281,10 @@ static inline void load_TLS(struct thread_struct *t,
unsigned cpu)
PVOP_VCALL2(cpu.load_tls, t, cpu);
}
-#ifdef CONFIG_X86_64
static inline void load_gs_index(unsigned int gs)
{
PVOP_VCALL1(cpu.load_gs_index, gs);
}
-#endif
static inline void write_ldt_entry(struct desc_struct *dt, int entry,
const void *desc)
@@ -375,50 +371,28 @@ static inline pte_t __pte(pteval_t val)
{
pteval_t ret;
- if (sizeof(pteval_t) > sizeof(long))
- ret = PVOP_CALLEE2(pteval_t, mmu.make_pte, val, (u64)val >> 32);
- else
- ret = PVOP_CALLEE1(pteval_t, mmu.make_pte, val);
+ ret = PVOP_CALLEE1(pteval_t, mmu.make_pte, val);
return (pte_t) { .pte = ret };
}
static inline pteval_t pte_val(pte_t pte)
{
- pteval_t ret;
-
- if (sizeof(pteval_t) > sizeof(long))
- ret = PVOP_CALLEE2(pteval_t, mmu.pte_val,
- pte.pte, (u64)pte.pte >> 32);
- else
- ret = PVOP_CALLEE1(pteval_t, mmu.pte_val, pte.pte);
-
- return ret;
+ return PVOP_CALLEE1(pteval_t, mmu.pte_val, pte.pte);
}
static inline pgd_t __pgd(pgdval_t val)
{
pgdval_t ret;
- if (sizeof(pgdval_t) > sizeof(long))
- ret = PVOP_CALLEE2(pgdval_t, mmu.make_pgd, val, (u64)val >> 32);
- else
- ret = PVOP_CALLEE1(pgdval_t, mmu.make_pgd, val);
+ ret = PVOP_CALLEE1(pgdval_t, mmu.make_pgd, val);
return (pgd_t) { ret };
}
static inline pgdval_t pgd_val(pgd_t pgd)
{
- pgdval_t ret;
-
- if (sizeof(pgdval_t) > sizeof(long))
- ret = PVOP_CALLEE2(pgdval_t, mmu.pgd_val,
- pgd.pgd, (u64)pgd.pgd >> 32);
- else
- ret = PVOP_CALLEE1(pgdval_t, mmu.pgd_val, pgd.pgd);
-
- return ret;
+ return PVOP_CALLEE1(pgdval_t, mmu.pgd_val, pgd.pgd);
}
#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
@@ -435,79 +409,48 @@ static inline pte_t ptep_modify_prot_start(struct
vm_area_struct *vma, unsigned
static inline void ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned
long addr,
pte_t *ptep, pte_t old_pte, pte_t pte)
{
-
- if (sizeof(pteval_t) > sizeof(long))
- /* 5 arg words */
- pv_ops.mmu.ptep_modify_prot_commit(vma, addr, ptep, pte);
- else
- PVOP_VCALL4(mmu.ptep_modify_prot_commit,
- vma, addr, ptep, pte.pte);
+ PVOP_VCALL4(mmu.ptep_modify_prot_commit, vma, addr, ptep, pte.pte);
}
static inline void set_pte(pte_t *ptep, pte_t pte)
{
- if (sizeof(pteval_t) > sizeof(long))
- PVOP_VCALL3(mmu.set_pte, ptep, pte.pte, (u64)pte.pte >> 32);
- else
- PVOP_VCALL2(mmu.set_pte, ptep, pte.pte);
+ PVOP_VCALL2(mmu.set_pte, ptep, pte.pte);
}
static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
- if (sizeof(pteval_t) > sizeof(long))
- /* 5 arg words */
- pv_ops.mmu.set_pte_at(mm, addr, ptep, pte);
- else
- PVOP_VCALL4(mmu.set_pte_at, mm, addr, ptep, pte.pte);
+ PVOP_VCALL4(mmu.set_pte_at, mm, addr, ptep, pte.pte);
}
static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
{
pmdval_t val = native_pmd_val(pmd);
- if (sizeof(pmdval_t) > sizeof(long))
- PVOP_VCALL3(mmu.set_pmd, pmdp, val, (u64)val >> 32);
- else
- PVOP_VCALL2(mmu.set_pmd, pmdp, val);
+ PVOP_VCALL2(mmu.set_pmd, pmdp, val);
}
-#if CONFIG_PGTABLE_LEVELS >= 3
static inline pmd_t __pmd(pmdval_t val)
{
pmdval_t ret;
- if (sizeof(pmdval_t) > sizeof(long))
- ret = PVOP_CALLEE2(pmdval_t, mmu.make_pmd, val, (u64)val >> 32);
- else
- ret = PVOP_CALLEE1(pmdval_t, mmu.make_pmd, val);
+ ret = PVOP_CALLEE1(pmdval_t, mmu.make_pmd, val);
return (pmd_t) { ret };
}
static inline pmdval_t pmd_val(pmd_t pmd)
{
- pmdval_t ret;
-
- if (sizeof(pmdval_t) > sizeof(long))
- ret = PVOP_CALLEE2(pmdval_t, mmu.pmd_val,
- pmd.pmd, (u64)pmd.pmd >> 32);
- else
- ret = PVOP_CALLEE1(pmdval_t, mmu.pmd_val, pmd.pmd);
-
- return ret;
+ return PVOP_CALLEE1(pmdval_t, mmu.pmd_val, pmd.pmd);
}
static inline void set_pud(pud_t *pudp, pud_t pud)
{
pudval_t val = native_pud_val(pud);
- if (sizeof(pudval_t) > sizeof(long))
- PVOP_VCALL3(mmu.set_pud, pudp, val, (u64)val >> 32);
- else
- PVOP_VCALL2(mmu.set_pud, pudp, val);
+ PVOP_VCALL2(mmu.set_pud, pudp, val);
}
-#if CONFIG_PGTABLE_LEVELS >= 4
+
static inline pud_t __pud(pudval_t val)
{
pudval_t ret;
@@ -572,29 +515,6 @@ static inline void p4d_clear(p4d_t *p4dp)
set_p4d(p4dp, __p4d(0));
}
-#endif /* CONFIG_PGTABLE_LEVELS == 4 */
-
-#endif /* CONFIG_PGTABLE_LEVELS >= 3 */
-
-#ifdef CONFIG_X86_PAE
-/* Special-case pte-setting operations for PAE, which can't update a
- 64-bit pte atomically */
-static inline void set_pte_atomic(pte_t *ptep, pte_t pte)
-{
- PVOP_VCALL3(mmu.set_pte_atomic, ptep, pte.pte, pte.pte >> 32);
-}
-
-static inline void pte_clear(struct mm_struct *mm, unsigned long addr,
- pte_t *ptep)
-{
- PVOP_VCALL3(mmu.pte_clear, mm, addr, ptep);
-}
-
-static inline void pmd_clear(pmd_t *pmdp)
-{
- PVOP_VCALL1(mmu.pmd_clear, pmdp);
-}
-#else /* !CONFIG_X86_PAE */
static inline void set_pte_atomic(pte_t *ptep, pte_t pte)
{
set_pte(ptep, pte);
@@ -610,7 +530,6 @@ static inline void pmd_clear(pmd_t *pmdp)
{
set_pmd(pmdp, __pmd(0));
}
-#endif /* CONFIG_X86_PAE */
#define __HAVE_ARCH_START_CONTEXT_SWITCH
static inline void arch_start_context_switch(struct task_struct *prev)
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 2474e434a6f7..b73d79091a0b 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -71,9 +71,7 @@ struct pv_info {
unsigned int kernel_rpl;
int shared_kernel_pmd;
-#ifdef CONFIG_X86_64
u16 extra_user_64bit_cs; /* __USER_CS if none */
-#endif
#endif
const char *name;
@@ -119,10 +117,8 @@ struct pv_cpu_ops {
void (*write_cr4)(unsigned long);
-#ifdef CONFIG_X86_64
unsigned long (*read_cr8)(void);
void (*write_cr8)(unsigned long);
-#endif
/* Segment descriptor handling */
void (*load_tr_desc)(void);
@@ -131,9 +127,7 @@ struct pv_cpu_ops {
void (*set_ldt)(const void *desc, unsigned entries);
unsigned long (*store_tr)(void);
void (*load_tls)(struct thread_struct *t, unsigned int cpu);
-#ifdef CONFIG_X86_64
void (*load_gs_index)(unsigned int idx);
-#endif
void (*write_ldt_entry)(struct desc_struct *ldt, int entrynum,
const void *desc);
void (*write_gdt_entry)(struct desc_struct *,
@@ -266,21 +260,11 @@ struct pv_mmu_ops {
struct paravirt_callee_save pgd_val;
struct paravirt_callee_save make_pgd;
-#if CONFIG_PGTABLE_LEVELS >= 3
-#ifdef CONFIG_X86_PAE
- void (*set_pte_atomic)(pte_t *ptep, pte_t pteval);
- void (*pte_clear)(struct mm_struct *mm, unsigned long addr,
- pte_t *ptep);
- void (*pmd_clear)(pmd_t *pmdp);
-
-#endif /* CONFIG_X86_PAE */
-
void (*set_pud)(pud_t *pudp, pud_t pudval);
struct paravirt_callee_save pmd_val;
struct paravirt_callee_save make_pmd;
-#if CONFIG_PGTABLE_LEVELS >= 4
struct paravirt_callee_save pud_val;
struct paravirt_callee_save make_pud;
@@ -293,10 +277,6 @@ struct pv_mmu_ops {
void (*set_pgd)(pgd_t *pgdp, pgd_t pgdval);
#endif /* CONFIG_PGTABLE_LEVELS >= 5 */
-#endif /* CONFIG_PGTABLE_LEVELS >= 4 */
-
-#endif /* CONFIG_PGTABLE_LEVELS >= 3 */
-
struct pv_lazy_ops lazy_mode;
/* dom0 ops */
diff --git a/arch/x86/include/asm/pgtable-3level_types.h
b/arch/x86/include/asm/pgtable-3level_types.h
index 33845d36897c..3955770d1a4d 100644
--- a/arch/x86/include/asm/pgtable-3level_types.h
+++ b/arch/x86/include/asm/pgtable-3level_types.h
@@ -20,12 +20,7 @@ typedef union {
} pte_t;
#endif /* !__ASSEMBLY__ */
-#ifdef CONFIG_PARAVIRT_XXL
-#define SHARED_KERNEL_PMD ((!static_cpu_has(X86_FEATURE_PTI) && \
- (pv_info.shared_kernel_pmd)))
-#else
#define SHARED_KERNEL_PMD (!static_cpu_has(X86_FEATURE_PTI))
-#endif
/*
* PGDIR_SHIFT determines what a top-level page table entry can map
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 2c57fffebf9b..a34246b01458 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1257,15 +1257,7 @@ static void generic_identify(struct cpuinfo_x86 *c)
* ESPFIX issue, we can change this.
*/
#ifdef CONFIG_X86_32
-# ifdef CONFIG_PARAVIRT_XXL
- do {
- extern void native_iret(void);
- if (pv_ops.cpu.iret == native_iret)
- set_cpu_bug(c, X86_BUG_ESPFIX);
- } while (0);
-# else
set_cpu_bug(c, X86_BUG_ESPFIX);
-# endif
#endif
}
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 06f6bb48d018..c9451267b4a3 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -284,10 +284,8 @@ struct pv_info pv_info = {
.kernel_rpl = 0,
.shared_kernel_pmd = 1, /* Only used when CONFIG_X86_PAE is set */
-#ifdef CONFIG_X86_64
.extra_user_64bit_cs = __USER_CS,
#endif
-#endif
};
/* 64-bit pagetable entries */
@@ -311,10 +309,8 @@ struct paravirt_patch_template pv_ops = {
.cpu.read_cr0 = native_read_cr0,
.cpu.write_cr0 = native_write_cr0,
.cpu.write_cr4 = native_write_cr4,
-#ifdef CONFIG_X86_64
.cpu.read_cr8 = native_read_cr8,
.cpu.write_cr8 = native_write_cr8,
-#endif
.cpu.wbinvd = native_wbinvd,
.cpu.read_msr = native_read_msr,
.cpu.write_msr = native_write_msr,
@@ -327,9 +323,7 @@ struct paravirt_patch_template pv_ops = {
.cpu.load_idt = native_load_idt,
.cpu.store_tr = native_store_tr,
.cpu.load_tls = native_load_tls,
-#ifdef CONFIG_X86_64
.cpu.load_gs_index = native_load_gs_index,
-#endif
.cpu.write_ldt_entry = native_write_ldt_entry,
.cpu.write_gdt_entry = native_write_gdt_entry,
.cpu.write_idt_entry = native_write_idt_entry,
@@ -339,9 +333,7 @@ struct paravirt_patch_template pv_ops = {
.cpu.load_sp0 = native_load_sp0,
-#ifdef CONFIG_X86_64
.cpu.usergs_sysret64 = native_usergs_sysret64,
-#endif
.cpu.iret = native_iret,
.cpu.swapgs = native_swapgs,
@@ -394,18 +386,11 @@ struct paravirt_patch_template pv_ops = {
.mmu.ptep_modify_prot_start = __ptep_modify_prot_start,
.mmu.ptep_modify_prot_commit = __ptep_modify_prot_commit,
-#if CONFIG_PGTABLE_LEVELS >= 3
-#ifdef CONFIG_X86_PAE
- .mmu.set_pte_atomic = native_set_pte_atomic,
- .mmu.pte_clear = native_pte_clear,
- .mmu.pmd_clear = native_pmd_clear,
-#endif
.mmu.set_pud = native_set_pud,
.mmu.pmd_val = PTE_IDENT,
.mmu.make_pmd = PTE_IDENT,
-#if CONFIG_PGTABLE_LEVELS >= 4
.mmu.pud_val = PTE_IDENT,
.mmu.make_pud = PTE_IDENT,
@@ -417,8 +402,6 @@ struct paravirt_patch_template pv_ops = {
.mmu.set_pgd = native_set_pgd,
#endif /* CONFIG_PGTABLE_LEVELS >= 5 */
-#endif /* CONFIG_PGTABLE_LEVELS >= 4 */
-#endif /* CONFIG_PGTABLE_LEVELS >= 3 */
.mmu.pte_val = PTE_IDENT,
.mmu.pgd_val = PTE_IDENT,
diff --git a/arch/x86/kernel/paravirt_patch_32.c
b/arch/x86/kernel/paravirt_patch_32.c
index de138d3912e4..f46a700d781a 100644
--- a/arch/x86/kernel/paravirt_patch_32.c
+++ b/arch/x86/kernel/paravirt_patch_32.c
@@ -1,23 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
#include <asm/paravirt.h>
-#ifdef CONFIG_PARAVIRT_XXL
-DEF_NATIVE(irq, irq_disable, "cli");
-DEF_NATIVE(irq, irq_enable, "sti");
-DEF_NATIVE(irq, restore_fl, "push %eax; popf");
-DEF_NATIVE(irq, save_fl, "pushf; pop %eax");
-DEF_NATIVE(cpu, iret, "iret");
-DEF_NATIVE(mmu, read_cr2, "mov %cr2, %eax");
-DEF_NATIVE(mmu, write_cr3, "mov %eax, %cr3");
-DEF_NATIVE(mmu, read_cr3, "mov %cr3, %eax");
-
-unsigned paravirt_patch_ident_64(void *insnbuf, unsigned len)
-{
- /* arg in %edx:%eax, return in %edx:%eax */
- return 0;
-}
-#endif
-
#if defined(CONFIG_PARAVIRT_SPINLOCKS)
DEF_NATIVE(lock, queued_spin_unlock, "movb $0, (%eax)");
DEF_NATIVE(lock, vcpu_is_preempted, "xor %eax, %eax");
@@ -28,22 +11,8 @@ extern bool pv_is_native_vcpu_is_preempted(void);
unsigned native_patch(u8 type, void *ibuf, unsigned long addr, unsigned len)
{
-#define PATCH_SITE(ops, x) \
- case PARAVIRT_PATCH(ops.x): \
- return paravirt_patch_insns(ibuf, len, start_##ops##_##x, end_##ops##_##x)
-
- switch (type) {
-#ifdef CONFIG_PARAVIRT_XXL
- PATCH_SITE(irq, irq_disable);
- PATCH_SITE(irq, irq_enable);
- PATCH_SITE(irq, restore_fl);
- PATCH_SITE(irq, save_fl);
- PATCH_SITE(cpu, iret);
- PATCH_SITE(mmu, read_cr2);
- PATCH_SITE(mmu, read_cr3);
- PATCH_SITE(mmu, write_cr3);
-#endif
#if defined(CONFIG_PARAVIRT_SPINLOCKS)
+ switch (type) {
case PARAVIRT_PATCH(lock.queued_spin_unlock):
if (pv_is_native_spin_unlock())
return paravirt_patch_insns(ibuf, len,
@@ -57,11 +26,10 @@ unsigned native_patch(u8 type, void *ibuf, unsigned long
addr, unsigned len)
start_lock_vcpu_is_preempted,
end_lock_vcpu_is_preempted);
break;
-#endif
default:
break;
}
-#undef PATCH_SITE
+#endif
return paravirt_patch_default(type, ibuf, addr, len);
}
--
2.16.4
On Mon, Jul 15, 2019 at 01:37:37PM +0200, Juergen Gross wrote:> The long term plan has been to replace Xen PV guests by PVH. The first > victim of that plan are now 32-bit PV guests, as those are used only > rather seldom these days. Xen on x86 requires 64-bit support and with > Grub2 now supporting PVH officially since version 2.04 there is no > need to keep 32-bit PV guest support alive in the Linux kernel. > Additionally Meltdown mitigation is not available in the kernel running > as 32-bit PV guest, so dropping this mode makes sense from security > point of view, too. > > Juergen Gross (2): > x86/xen: remove 32-bit Xen PV guest support > x86/paravirt: remove 32-bit support from PARAVIRT_XXLHooray!
On 15.07.19 14:32, Peter Zijlstra wrote:> On Mon, Jul 15, 2019 at 01:37:37PM +0200, Juergen Gross wrote: >> The long term plan has been to replace Xen PV guests by PVH. The first >> victim of that plan are now 32-bit PV guests, as those are used only >> rather seldom these days. Xen on x86 requires 64-bit support and with >> Grub2 now supporting PVH officially since version 2.04 there is no >> need to keep 32-bit PV guest support alive in the Linux kernel. >> Additionally Meltdown mitigation is not available in the kernel running >> as 32-bit PV guest, so dropping this mode makes sense from security >> point of view, too. >> >> Juergen Gross (2): >> x86/xen: remove 32-bit Xen PV guest support >> x86/paravirt: remove 32-bit support from PARAVIRT_XXL > > Hooray! >Always a pleasure to cheer the community up by sending Xen patches. :-D Juergen
Juergen Gross <jgross at suse.com> writes:> The long term plan has been to replace Xen PV guests by PVH. The first > victim of that plan are now 32-bit PV guests, as those are used only > rather seldom these days. Xen on x86 requires 64-bit support and with > Grub2 now supporting PVH officially since version 2.04 there is no > need to keep 32-bit PV guest support alive in the Linux kernel. > Additionally Meltdown mitigation is not available in the kernel running > as 32-bit PV guest, so dropping this mode makes sense from security > point of view, too.Normally we have a deprecation period for feature removals like this. You would make the kernel print a warning for some releases, and when no user complains you can then remove. If a user complains you can't. -Andi
On Mon, Jul 15, 2019 at 9:34 AM Andi Kleen <ak at linux.intel.com> wrote:> > Juergen Gross <jgross at suse.com> writes: > > > The long term plan has been to replace Xen PV guests by PVH. The first > > victim of that plan are now 32-bit PV guests, as those are used only > > rather seldom these days. Xen on x86 requires 64-bit support and with > > Grub2 now supporting PVH officially since version 2.04 there is no > > need to keep 32-bit PV guest support alive in the Linux kernel. > > Additionally Meltdown mitigation is not available in the kernel running > > as 32-bit PV guest, so dropping this mode makes sense from security > > point of view, too. > > Normally we have a deprecation period for feature removals like this. > You would make the kernel print a warning for some releases, and when > no user complains you can then remove. If a user complains you can't. >As I understand it, the kernel rules do allow changes like this even if there's a complaint: this is a patch that removes what is effectively hardware support. If the maintenance cost exceeds the value, then removal is fair game. (Obviously we weight the value to preserving compatibility quite highly, but in this case, Xen dropped 32-bit hardware support a long time ago. If the Xen hypervisor says that 32-bit PV guest support is deprecated, it's deprecated.) That being said, a warning might not be a bad idea. What's the current status of this in upstream Xen?