[PATCH v4 40/75] x86/sev-es: Setup early #VC handler

Joerg Roedel
Tue, 14 Jul 2020 12:08:42 -0000

Setup an early handler for #VC exceptions. There is no GHCB mapped
yet, so just re-use the vc_no_ghcb_handler. It can only handle CPUID
exit-codes, but that should be enough to get the kernel through
verify_cpu() and __startup_64() until it runs on virtual addresses.

Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 arch/x86/include/asm/processor.h |  1 +
 arch/x86/include/asm/sev-es.h    |  3 +++
 arch/x86/kernel/head64.c         | 31 +++++++++++++++++++++++++
 arch/x86/kernel/head_64.S        | 39 ++++++++++++++++++++++++++++++++
 4 files changed, 74 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 03b7c4ca425a..e6a029b76b3d 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -756,6 +756,7 @@ extern int sysenter_setup(void);

 /* Defined in head.S */
 extern struct desc_ptr		early_gdt_descr;
+extern struct desc_ptr		early_idt_descr;

 extern void switch_to_new_gdt(int);
 extern void load_direct_gdt(int);
diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 7c0807b84546..ec0e112a742b 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -73,4 +73,7 @@ static inline u64 lower_bits(u64 val, unsigned int bits)
 	return (val & mask);
 }

+/* Early IDT entry points for #VC handler */
+extern void vc_no_ghcb(void);
+
 #endif
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 32080e34ba92..9ea8a0437b66 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -38,6 +38,7 @@
 #include <asm/fixmap.h>
 #include <asm/extable.h>
 #include <asm/trapnr.h>
+#include <asm/sev-es.h>

 /*
  * Manage page tables very early on.
@@ -537,3 +538,33 @@ void __head early_idt_setup_early_handler(unsigned long
descr_addr, unsigned lon
 		native_write_idt_entry(idt, i, &desc);
 	}
 }
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+static void __head set_early_idt_handler(gate_desc *idt, int n, void *handler)
+{
+	struct idt_data data;
+	gate_desc desc;
+
+	init_idt_data(&data, n, handler);
+	idt_init_desc(&desc, &data);
+	native_write_idt_entry(idt, n, &desc);
+}
+#endif
+
+void __head early_idt_setup(struct desc_ptr *descr, unsigned long physbase)
+{
+	gate_desc *idt = (gate_desc *)descr->address;
+	void __maybe_unused *handler;
+
+	idt = fixup_pointer(idt, physbase);
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+	/* VMM Communication Exception */
+	handler = fixup_pointer(vc_no_ghcb, physbase);
+	set_early_idt_handler(idt, X86_TRAP_VC, handler);
+#endif
+
+	/* Initialize IDT descriptor and load IDT */
+	early_idt_descr.address = (unsigned long)idt;
+	native_load_idt(&early_idt_descr);
+}
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 86473d49619d..3bd4c36d1d36 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -93,6 +93,15 @@ SYM_CODE_START_NOALIGN(startup_64)
 .Lon_kernel_cs:
 	UNWIND_HINT_EMPTY

+	/* Setup IDT - Needed for SEV-ES */
+	pushq	%rsi
+	/* early_idt_setup - first parameter */
+	leaq	idt_descr(%rip), %rdi
+	/* early_idt_setup - second parameter */
+	leaq	_text(%rip), %rsi
+	call	early_idt_setup
+	popq	%rsi
+
 	/* Sanitize CPU configuration */
 	call verify_cpu

@@ -382,6 +391,33 @@ SYM_CODE_START_LOCAL(early_idt_handler_common)
 	jmp restore_regs_and_return_to_kernel
 SYM_CODE_END(early_idt_handler_common)

+#ifdef CONFIG_AMD_MEM_ENCRYPT
+/*
+ * VC Exception handler used during very early boot. The
+ * early_idt_handler_array can't be used because it returns via the
+ * paravirtualized INTERRUPT_RETURN and pv-ops don't work that early.
+ */
+SYM_CODE_START_NOALIGN(vc_no_ghcb)
+	UNWIND_HINT_IRET_REGS offset=8
+
+	/* Build pt_regs */
+	PUSH_AND_CLEAR_REGS
+
+	/* Call C handler */
+	movq    %rsp, %rdi
+	movq	ORIG_RAX(%rsp), %rsi
+	call    do_vc_no_ghcb
+
+	/* Unwind pt_regs */
+	POP_REGS
+
+	/* Remove Error Code */
+	addq    $8, %rsp
+
+	/* Pure iret required here - don't use INTERRUPT_RETURN */
+	iretq
+SYM_CODE_END(vc_no_ghcb)
+#endif

 #define SYM_DATA_START_PAGE_ALIGNED(name)			\
 	SYM_START(name, SYM_L_GLOBAL, .balign PAGE_SIZE)
@@ -523,6 +559,9 @@ SYM_DATA_END(level1_fixmap_pgt)
 SYM_DATA(early_gdt_descr,		.word GDT_ENTRIES*8-1)
 SYM_DATA_LOCAL(early_gdt_descr_base,	.quad INIT_PER_CPU_VAR(gdt_page))

+SYM_DATA(early_idt_descr,		.word NUM_EXCEPTION_VECTORS * 16)
+SYM_DATA_LOCAL(early_idt_descr_base,	.quad 0)
+
 	.align 16
 /* This must match the first entry in level2_kernel_pgt */
 SYM_DATA(phys_base, .quad 0x0)
--
2.27.0