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AJvYcCV6zxk+dcY5ilByJCpn9seUd1IVptXgDf8A2F3bTv4/o69XC3AdWVxKdqBZA8b4dogqJNSDa2MObuBatjscggkgkBi4LoIgzff0xA== X-Gm-Message-State: AOJu0YzjKT1ZvOu7XHEsRC1g2jCmz7F5FpEooRQK+YKURyHh20SN/Evl UhRn2zK3BeT3/NemCQ1YqQLsmYyNMsQCyIPFFZhv/ZrOYDVyxa3Ic6reQLF/dZ1JUqappFWsELi hzw== X-Google-Smtp-Source: AGHT+IF06EpTOwvZeQGKlqPQtXFzYGfZPqUfmBFZuyaYdLAzcsdi+7awfJdAqckqz+IcAQhBBvcZ3k/AgAM= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6902:1205:b0:de5:2325:72ac with SMTP id s5-20020a056902120500b00de5232572acmr1331874ybu.6.1714004238029; Wed, 24 Apr 2024 17:17:18 -0700 (PDT) Date: Wed, 24 Apr 2024 17:17:16 -0700 In-Reply-To: <20240421180122.1650812-18-michael.roth@amd.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240421180122.1650812-1-michael.roth@amd.com> <20240421180122.1650812-18-michael.roth@amd.com> Message-ID: Subject: Re: [PATCH v14 17/22] KVM: SEV: Avoid WBINVD for HVA-based MMU notifications for SNP From: Sean Christopherson To: Michael Roth Cc: kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, pbonzini@redhat.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com Content-Type: text/plain; charset="us-ascii" On Sun, Apr 21, 2024, Michael Roth wrote: > From: Ashish Kalra > > With SNP/guest_memfd, private/encrypted memory should not be mappable, > and MMU notifications for HVA-mapped memory will only be relevant to > unencrypted guest memory. Therefore, the rationale behind issuing a > wbinvd_on_all_cpus() in sev_guest_memory_reclaimed() should not apply > for SNP guests and can be ignored. > > Signed-off-by: Ashish Kalra > Reviewed-by: Paolo Bonzini > [mdr: Add some clarifications in commit] > Signed-off-by: Michael Roth > --- > arch/x86/kvm/svm/sev.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index 243369e302f4..cf00a811aca5 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -3042,7 +3042,14 @@ static void sev_flush_encrypted_page(struct kvm_vcpu *vcpu, void *va) > > void sev_guest_memory_reclaimed(struct kvm *kvm) > { > - if (!sev_guest(kvm)) > + /* > + * With SNP+gmem, private/encrypted memory should be Not should, *is*. > + * unreachable via the hva-based mmu notifiers. Additionally, > + * for shared->private translations, H/W coherency will ensure > + * first guest access to the page would clear out any existing > + * dirty copies of that cacheline. I don't see how this second part is relevant. > + */ > + if (!sev_guest(kvm) || sev_snp_guest(kvm)) > return; > > wbinvd_on_all_cpus(); > -- > 2.25.1 >