linux-kernel - [PATCH 5.0 100/122] KVM: VMX: Save RSI to an unused output in the vCPU-run asm blob

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Date:   Mon,  6 May 2019 16:32:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.0 100/122] KVM: VMX: Save RSI to an unused output in the vCPU-run asm blob

From: Sean Christopherson <sean.j.christopherson@...el.com>

commit f3689e3f17f064fd4cd5f0cb01ae2395c94f39d9 upstream.

RSI is clobbered by the vCPU-run asm blob, but it's not marked as such,
probably because GCC doesn't let you mark inputs as clobbered.  "Save"
RSI to a dummy output so that GCC recognizes it as being clobbered.

Fixes: 773e8a0425c9 ("x86/kvm: use Enlightened VMCS when running on Hyper-V")
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/vmx/vmx.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6465,7 +6465,7 @@ static void __vmx_vcpu_run(struct kvm_vc
 		"xor %%edi, %%edi \n\t"
 		"xor %%ebp, %%ebp \n\t"
 		"pop  %%" _ASM_BP "; pop  %%" _ASM_DX " \n\t"
-	      : ASM_CALL_CONSTRAINT
+	      : ASM_CALL_CONSTRAINT, "=S"((int){0})
 	      : "c"(vmx), "d"((unsigned long)HOST_RSP), "S"(evmcs_rsp),
 		[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
 		[fail]"i"(offsetof(struct vcpu_vmx, fail)),