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([2001:b07:6468:f312:1c09:f536:3de6:228c]) by smtp.googlemail.com with ESMTPSA id y16-20020adfd090000000b0022ae401e9e0sm1285436wrh.78.2022.10.27.08.03.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Oct 2022 08:03:10 -0700 (PDT) Message-ID: <24768aa3-0e2e-6d29-2749-9d74a26f9205@redhat.com> Date: Thu, 27 Oct 2022 17:03:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.1 Subject: Re: [PATCH v2 03/16] KVM: x86: Always use non-compat vcpu_runstate_info size for gfn=>pfn cache Content-Language: en-US To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Michal Luczaj , David Woodhouse References: <20221013211234.1318131-1-seanjc@google.com> <20221013211234.1318131-4-seanjc@google.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/27/22 16:44, Sean Christopherson wrote: >> - long mode cannot be changed after the shared info page is enabled (which >> makes sense because the shared info page also has a compat version) > > How is this not introducing an additional restriction? This seems way more > onerous than what is effectively a revert. > >> - the caches must be activated after the shared info page (which enforces >> that the vCPU attributes are set after the VM attributes) >> >> This is technically a userspace API break, but nobody is really using this >> API outside Amazon so... Patches coming after I finish testing. > > It's not just userspace break, it affects the guest ABI as well. Yes, I was talking of the VMM here; additional restrictions are fine there. The guests however should be compatible with Xen, so you also need to re-activate the cache after the hypercall page is written, but that's two lines of code. Paolo