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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id f17sm4978983wme.22.2020.10.21.11.00.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Oct 2020 11:00:49 -0700 (PDT) Subject: Re: [PATCH v2 07/20] kvm: x86/mmu: Support zapping SPTEs in the TDP MMU To: Yu Zhang Cc: Ben Gardon , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Cannon Matthews , Peter Xu , Sean Christopherson , Peter Shier , Peter Feiner , Junaid Shahid , Jim Mattson , Yulei Zhang , Wanpeng Li , Vitaly Kuznetsov , Xiao Guangrong References: <20201014182700.2888246-1-bgardon@google.com> <20201014182700.2888246-8-bgardon@google.com> <20201021150225.2eeriqlffqnsm4b3@linux.intel.com> <6985f630-3b2a-75f5-5b55-bd76cf32f20b@redhat.com> <20201021172409.aids3y2mlyx776lx@linux.intel.com> From: Paolo Bonzini Message-ID: <0f2e00fe-4f30-88d3-e345-089f1afc4fb9@redhat.com> Date: Wed, 21 Oct 2020 20:00:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201021172409.aids3y2mlyx776lx@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/10/20 19:24, Yu Zhang wrote: > On Wed, Oct 21, 2020 at 07:20:15PM +0200, Paolo Bonzini wrote: >> On 21/10/20 17:02, Yu Zhang wrote: >>>> void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root) >>>> { >>>> + gfn_t max_gfn = 1ULL << (boot_cpu_data.x86_phys_bits - PAGE_SHIFT); >>>> + >>> boot_cpu_data.x86_phys_bits is the host address width. Value of the guest's >>> may vary. So maybe we should just traverse the memslots and zap the gfn ranges >>> in each of them? >>> >> >> It must be smaller than the host value for two-dimensional paging, though. > > Yes. And using boot_cpu_data.x86_phys_bits works, but won't it be somewhat > overkilling? E.g. for a host with 46 bits and a guest with 39 bits width? It would go quickly through extra memory space because the PML4E entries above the first would be empty. So it's just 511 comparisons. Paolo