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Subject[PATCH 4/7] x86/boot/compressed/64: Add 32-bit boot #VC handler
Date
From: Joerg Roedel <jroedel@suse.de>

Add a #VC exception handler which is used when the kernel still executes
in protected mode. This boot-path already uses CPUID, which will cause #VC
exceptions in an SEV-ES guest.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/boot/compressed/head_64.S | 6 ++
arch/x86/boot/compressed/mem_encrypt.S | 77 +++++++++++++++++++++++++-
2 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 8deeec78cdb4..eadaa0a082b8 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -34,6 +34,7 @@
#include <asm/asm-offsets.h>
#include <asm/bootparam.h>
#include <asm/desc_defs.h>
+#include <asm/trapnr.h>
#include "pgtable.h"

/*
@@ -856,6 +857,11 @@ SYM_FUNC_START(startup32_set_idt_entry)
SYM_FUNC_END(startup32_set_idt_entry)

SYM_FUNC_START(startup32_load_idt)
+ /* #VC handler */
+ leal rva(startup32_vc_handler)(%ebp), %eax
+ movl $X86_TRAP_VC, %edx
+ call startup32_set_idt_entry
+
/* Load IDT */
leal rva(boot32_idt)(%ebp), %eax
movl %eax, rva(boot32_idt_desc+2)(%ebp)
diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
index aa561795efd1..350ecb56c7e4 100644
--- a/arch/x86/boot/compressed/mem_encrypt.S
+++ b/arch/x86/boot/compressed/mem_encrypt.S
@@ -67,10 +67,85 @@ SYM_FUNC_START(get_sev_encryption_bit)
ret
SYM_FUNC_END(get_sev_encryption_bit)

+/*
+ * Emit code to request an CPUID register from the Hypervisor using
+ * the MSR-based protocol.
+ *
+ * fn: The register containing the CPUID function
+ * reg: Register requested
+ * 1 = EAX
+ * 2 = EBX
+ * 3 = ECX
+ * 4 = EDX
+ *
+ * Result is in EDX. Jumps to .Lfail on error
+ */
+.macro SEV_ES_REQ_CPUID fn:req reg:req
+ /* Request CPUID[%ebx].EAX */
+ movl $\reg, %eax
+ shll $30, %eax
+ orl $0x00000004, %eax
+ movl \fn, %edx
+ movl $MSR_AMD64_SEV_ES_GHCB, %ecx
+ wrmsr
+ rep; vmmcall
+ rdmsr
+ /* Check response code */
+ andl $0xfff, %eax
+ cmpl $5, %eax
+ jne .Lfail
+ /* All good */
+.endm
+
+SYM_CODE_START(startup32_vc_handler)
+ pushl %eax
+ pushl %ebx
+ pushl %ecx
+ pushl %edx
+
+ /* Keep CPUID function in %ebx */
+ movl %eax, %ebx
+
+ /* Check if error-code == SVM_EXIT_CPUID */
+ cmpl $0x72, 16(%esp)
+ jne .Lfail
+
+ /* Request CPUID[%ebx].EAX */
+ SEV_ES_REQ_CPUID fn=%ebx reg=0
+ movl %edx, 12(%esp)
+
+ /* Request CPUID[%ebx].EBX */
+ SEV_ES_REQ_CPUID fn=%ebx reg=1
+ movl %edx, 8(%esp)
+
+ /* Request CPUID[%ebx].ECX */
+ SEV_ES_REQ_CPUID fn=%ebx reg=2
+ movl %edx, 4(%esp)
+
+ /* Request CPUID[%ebx].EDX */
+ SEV_ES_REQ_CPUID fn=%ebx reg=3
+ movl %edx, (%esp)
+
+ popl %edx
+ popl %ecx
+ popl %ebx
+ popl %eax
+
+ /* Remove error code */
+ addl $4, %esp
+
+ /* Jump over CPUID instruction */
+ addl $2, (%esp)
+
+ iret
+.Lfail:
+ hlt
+ jmp .Lfail
+SYM_CODE_END(startup32_vc_handler)
+
.code64

#include "../../kernel/sev_verify_cbit.S"
-
SYM_FUNC_START(set_sev_encryption_mask)
#ifdef CONFIG_AMD_MEM_ENCRYPT
push %rbp
--
2.30.0
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