linux-kernel - [PATCH 2/2] KVM: SVM: drop useless cpumask_test_cpu() in pre_sev

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Message-ID: <20250811203041.61622-3-yury.norov@gmail.com>
Date: Mon, 11 Aug 2025 16:30:40 -0400
From: Yury Norov <yury.norov@...il.com>
To: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Yury Norov <yury.norov@...il.com>,
	Zheyun Shen <szy0127@...u.edu.cn>
Subject: [PATCH 2/2] KVM: SVM: drop useless cpumask_test_cpu() in pre_sev_run()

Testing cpumask for a CPU to be cleared just before setting the exact
same CPU is useless because the end result is always the same: CPU is
set.

While there, switch CPU setter to a non-atomic version. Atomicity is
useless here because sev_writeback_caches() ends up with a plain
for_each_cpu() loop in smp_call_function_many_cond(), which is not
atomic by nature.

Fixes: 6f38f8c57464 ("KVM: SVM: Flush cache only on CPUs running SEV guest")
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 arch/x86/kvm/svm/sev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 49d7557de8bc..8170674d39c1 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3498,8 +3498,7 @@ int pre_sev_run(struct vcpu_svm *svm, int cpu)
 	 * have encrypted, dirty data in the cache, and flush caches only for
 	 * CPUs that have entered the guest.
 	 */
-	if (!cpumask_test_cpu(cpu, to_kvm_sev_info(kvm)->have_run_cpus))
-		cpumask_set_cpu(cpu, to_kvm_sev_info(kvm)->have_run_cpus);
+	__cpumask_set_cpu(cpu, to_kvm_sev_info(kvm)->have_run_cpus);
 
 	/* Assign the asid allocated with this SEV guest */
 	svm->asid = asid;
-- 
2.43.0