linux-kernel - [PATCH 4/4 v3] KVM: SVM: Don't flush cache if hardware enforces cache coherency across encryption domains

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Message-Id: <20200911192601.9591-5-krish.sadhukhan@oracle.com>
Date:   Fri, 11 Sep 2020 19:26:01 +0000
From:   Krish Sadhukhan <krish.sadhukhan@...cle.com>
To:     kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, jmattson@...gle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        sean.j.christopherson@...el.com, vkuznets@...hat.com,
        wanpengli@...cent.com, joro@...tes.org,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, hpa@...or.com
Subject: [PATCH 4/4 v3] KVM: SVM: Don't flush cache if hardware enforces cache coherency across encryption domains

In some hardware implementations, coherency between the encrypted and
unencrypted mappings of the same physical page in a VM is enforced. In such a
system, it is not required for software to flush the VM's page from all CPU
caches in the system prior to changing the value of the C-bit for the page.

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@...cle.com>
---
 arch/x86/kvm/svm/sev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 402dc4234e39..8aa2209f2637 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -384,7 +384,8 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages)
 	uint8_t *page_virtual;
 	unsigned long i;
 
-	if (npages == 0 || pages == NULL)
+	if (this_cpu_has(X86_FEATURE_HW_CACHE_COHERENCY) || npages == 0 ||
+	    pages == NULL)
 		return;
 
 	for (i = 0; i < npages; i++) {
-- 
2.18.4