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From: Nathan Chancellor <natechancellor@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	Nick Desaulniers <ndesaulniers@google.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>
Subject: [PATCH] KVM: SVM: Add register operand to vmsave call in sev_es_vcpu_load
Date: Fri, 18 Dec 2020 23:37:11 -0700
Message-ID: <20201219063711.3526947-1-natechancellor@gmail.com> (raw)

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
         vmsave
         ^
 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")
Link: https://reviews.llvm.org/D93524
Link: https://github.com/ClangBuiltLinux/linux/issues/1216
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 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
-- 
2.30.0.rc0


             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-19  6:37 Nathan Chancellor [this message]
2020-12-21 17:48 ` Sean Christopherson
2020-12-21 18:10   ` Sean Christopherson
2020-12-21 18:12 ` Paolo Bonzini

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