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Date:   Fri, 18 Dec 2020 23:37:11 -0700
From:   Nathan Chancellor <>
To:     Paolo Bonzini <>
Cc:     Tom Lendacky <>,
        Sean Christopherson <>,
        Vitaly Kuznetsov <>,
        Wanpeng Li <>,
        Jim Mattson <>,
        Joerg Roedel <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,,,,,
        Nick Desaulniers <>,
        Sami Tolvanen <>,
        Nathan Chancellor <>
Subject: [PATCH] KVM: SVM: Add register operand to vmsave call in sev_es_vcpu_load

When using LLVM's integrated assembler (LLVM_IAS=1) while building
x86_64_defconfig + CONFIG_KVM=y + CONFIG_KVM_AMD=y, the following build
error occurs:

 $ make LLVM=1 LLVM_IAS=1 arch/x86/kvm/svm/sev.o
 arch/x86/kvm/svm/sev.c:2004:15: error: too few operands for instruction
         asm volatile(__ex("vmsave") : : "a" (__sme_page_pa(sd->save_area)) : "memory");
 arch/x86/kvm/svm/sev.c:28:17: note: expanded from macro '__ex'
 #define __ex(x) __kvm_handle_fault_on_reboot(x)
 ./arch/x86/include/asm/kvm_host.h:1646:10: note: expanded from macro '__kvm_handle_fault_on_reboot'
         "666: \n\t"                                                     \
 <inline asm>:2:2: note: instantiated into assembly here
 1 error generated.

This happens because LLVM currently does not support calling vmsave
without the fixed register operand (%rax for 64-bit and %eax for
32-bit). This will be fixed in LLVM 12 but the kernel currently supports
LLVM 10.0.1 and newer so this needs to be handled.

Add the proper register using the _ASM_AX macro, which matches the
vmsave call in vmenter.S.

Fixes: 861377730aa9 ("KVM: SVM: Provide support for SEV-ES vCPU loading")
Signed-off-by: Nathan Chancellor <>
 arch/x86/kvm/svm/sev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index e57847ff8bd2..958370758ed0 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2001,7 +2001,7 @@ void sev_es_vcpu_load(struct vcpu_svm *svm, int cpu)
 	 * of which one step is to perform a VMLOAD. Since hardware does not
 	 * perform a VMSAVE on VMRUN, the host savearea must be updated.
-	asm volatile(__ex("vmsave") : : "a" (__sme_page_pa(sd->save_area)) : "memory");
+	asm volatile(__ex("vmsave %%"_ASM_AX) : : "a" (__sme_page_pa(sd->save_area)) : "memory");
 	 * Certain MSRs are restored on VMEXIT, only save ones that aren't

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