linux-kernel - [PATCH 4/8] KVM: SVM: Clobber RAX instead of RBX when discarding spec_ctrl

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Message-ID: <20240223204233.3337324-5-seanjc@google.com>
Date: Fri, 23 Feb 2024 12:42:29 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Michael Roth <michael.roth@....com>, 
	Alexey Kardashevskiy <aik@....com>
Subject: [PATCH 4/8] KVM: SVM: Clobber RAX instead of RBX when discarding spec_ctrl_intercepted

POP @spec_ctrl_intercepted into RAX instead of RBX when discarding it from
the stack so that __svm_sev_es_vcpu_run() doesn't modify any non-volatile
registers.  __svm_sev_es_vcpu_run() doesn't return a value, and RAX is
already are clobbered multiple times in the #VMEXIT path.

This will allowing using the host save area to save/restore non-volatile
registers in __svm_sev_es_vcpu_run().

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/vmenter.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 0026b4a56d25..edbaadaacba7 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -350,8 +350,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
 	 */
 	UNTRAIN_RET_VM
 
-	/* "Pop" @spec_ctrl_intercepted.  */
-	pop %rbx
+	/* "Pop" and discard @spec_ctrl_intercepted. */
+	pop %rax
 
 	pop %rbx
 
-- 
2.44.0.rc0.258.g7320e95886-goog