linux-kernel - [PATCH 1/2] KVM: SVM: don't check have_run_cpus in sev_writeback

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Message-ID: <20250811203041.61622-2-yury.norov@gmail.com>
Date: Mon, 11 Aug 2025 16:30:39 -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 1/2] KVM: SVM: don't check have_run_cpus in sev_writeback_caches()

From: Yury Norov (NVIDIA) <yury.norov@...il.com>

Before calling wbnoinvd_on_cpus_mask(), the function checks the cpumask
for emptiness. It's useless, as the following wbnoinvd_on_cpus_mask()
ends up with smp_call_function_many_cond(), which handles empty cpumask
correctly.

While there, move function-wide comment on top of the function.

Fixes: 6f38f8c57464 ("KVM: SVM: Flush cache only on CPUs running SEV guest")
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
---
 arch/x86/kvm/svm/sev.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 2fbdebf79fbb..49d7557de8bc 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -716,15 +716,12 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages)
 	}
 }
 
+/*
+ * The caller is responsible for ensuring correctness if the mask
+ * can be modified, e.g. if a CPU could be doing VMRUN.
+ */
 static void sev_writeback_caches(struct kvm *kvm)
 {
-	/*
-	 * Note, the caller is responsible for ensuring correctness if the mask
-	 * can be modified, e.g. if a CPU could be doing VMRUN.
-	 */
-	if (cpumask_empty(to_kvm_sev_info(kvm)->have_run_cpus))
-		return;
-
 	/*
 	 * Ensure that all dirty guest tagged cache entries are written back
 	 * before releasing the pages back to the system for use.  CLFLUSH will
-- 
2.43.0