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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id r1sm2625150eje.51.2020.12.04.00.48.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Dec 2020 00:48:59 -0800 (PST) Subject: Re: [PATCH] kvm: x86/mmu: Use cpuid to determine max gfn To: Sean Christopherson , Rick Edgecombe Cc: vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, bgardon@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20201203231120.27307-1-rick.p.edgecombe@intel.com> From: Paolo Bonzini Message-ID: <9f527b7b-96de-6657-aa48-8de401f5083e@redhat.com> Date: Fri, 4 Dec 2020 09:48:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/12/20 01:43, Sean Christopherson wrote: > On Thu, Dec 03, 2020, Rick Edgecombe wrote: >> In the TDP MMU, use shadow_phys_bits to dermine the maximum possible GFN >> mapped in the guest for zapping operations. boot_cpu_data.x86_phys_bits >> may be reduced in the case of HW features that steal HPA bits for other >> purposes. However, this doesn't necessarily reduce GPA space that can be >> accessed via TDP. So zap based on a maximum gfn calculated with MAXPHYADDR >> retrieved from CPUID. This is already stored in shadow_phys_bits, so use >> it instead of x86_phys_bits. >> >> Fixes: faaf05b00aec ("kvm: x86/mmu: Support zapping SPTEs in the TDP MMU") >> Signed-off-by: Rick Edgecombe > > Dang, in hindsight it'd be nice if KVM_CAP_SMALLER_MAXPHYADDR allowed explicitly > setting the max MAXPHYADDR for an entire VM instead of being a simple toggle. > E.g. TDX and SEV-ES likely could also make use of "what's this VM's max GPA?". > > Reviewed-by: Sean Christopherson > Queued, thanks. Paolo