linux-kernel - [PATCH 5/5] KVM: SVM: Add a mutex to dump

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Message-ID: <a880678afd9488e1dd6017445802712f7c02cc6d.1742477213.git.thomas.lendacky@amd.com>
Date: Thu, 20 Mar 2025 08:26:53 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>
CC: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson
	<seanjc@...gle.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, "Thomas
 Gleixner" <tglx@...utronix.de>, Michael Roth <michael.roth@....com>
Subject: [PATCH 5/5] KVM: SVM: Add a mutex to dump_vmcb() to prevent concurrent output

If multiple VMRUN instructions fail, resulting in calls to dump_vmcb(),
the output can become interleaved and it is impossible to identify which
line of output belongs to which VMCB. Add a mutex to dump_vmcb() so that
the output is serialized.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/kvm/svm/svm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 99f2d9de6ce2..5b62ac06a19e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -29,6 +29,7 @@
 #include <linux/cc_platform.h>
 #include <linux/smp.h>
 #include <linux/string_choices.h>
+#include <linux/mutex.h>
 
 #include <asm/apic.h>
 #include <asm/perf_event.h>
@@ -249,6 +250,8 @@ static unsigned long iopm_base;
 
 DEFINE_PER_CPU(struct svm_cpu_data, svm_data);
 
+static DEFINE_MUTEX(vmcb_dump_mutex);
+
 /*
  * Only MSR_TSC_AUX is switched via the user return hook.  EFER is switched via
  * the VMCB, and the SYSCALL/SYSENTER MSRs are handled by VMLOAD/VMSAVE.
@@ -3385,6 +3388,8 @@ static void dump_vmcb(struct kvm_vcpu *vcpu)
 		return;
 	}
 
+	guard(mutex)(&vmcb_dump_mutex);
+
 	vm_type = sev_snp_guest(vcpu->kvm) ? "SEV-SNP" :
 		  sev_es_guest(vcpu->kvm) ? "SEV-ES" :
 		  sev_guest(vcpu->kvm) ? "SEV" : "SVM";
-- 
2.46.2