Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Krish Sadhukhan <krish.sadhukhan@oracle.com>
To:     kvm@vger.kernel.org
Cc:     pbonzini@redhat.com, jmattson@google.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        sean.j.christopherson@intel.com, vkuznets@redhat.com,
        wanpengli@tencent.com, joro@8bytes.org,
        dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
        linux-kernel@vger.kernel.org, hpa@zytor.com
Subject: [PATCH 4/4 v3] KVM: SVM: Don't flush cache if hardware enforces cache coherency across encryption domains
Date:   Fri, 11 Sep 2020 19:26:01 +0000
Message-Id: <20200911192601.9591-5-krish.sadhukhan@oracle.com>
In-Reply-To: <20200911192601.9591-1-krish.sadhukhan@oracle.com>
References: <20200911192601.9591-1-krish.sadhukhan@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@oracle.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