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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id cw14sm8224396edb.8.2021.03.08.14.51.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Mar 2021 14:51:47 -0800 (PST) Subject: Re: [PATCH 03/28] KVM: nSVM: inject exceptions via svm_check_nested_events To: Sean Christopherson Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, vkuznets@redhat.com, mlevitsk@redhat.com, Jim Mattson References: <006be822-697e-56d5-84a7-fa51f5087a34@redhat.com> From: Paolo Bonzini Message-ID: <30846470-28e2-c05d-21c7-9ad5631bf821@redhat.com> Date: Mon, 8 Mar 2021 23:51:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 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 08/03/21 21:43, Sean Christopherson wrote: > On Mon, Mar 08, 2021, Paolo Bonzini wrote: >> On 08/03/21 17:44, Sean Christopherson wrote: >>> VMCALL is also probably ok >>> in most scenarios, but patching L2's code from L0 KVM is sketchy. >> >> I agree that patching is sketchy and I'll send a patch. However... >> >>>> The same is true for the VMware #GP interception case. >>> >>> I highly doubt that will ever work out as intended for the modified IO #GP >>> behavior. The only way emulating #GP in L2 is correct if L1 wants to pass >>> through the capabilities to L2, i.e. the I/O access isn't intercepted by L1. >>> That seems unlikely. >> >> ... not all hypervisors trap everything. In particular in this case the >> VMCS12 I/O permission bitmap should be consulted (which we do in >> vmx_check_intercept_io), but if the I/O is not trapped by L1 it should >> bypass the IOPL and TSS-bitmap checks in my opinion. > > I agree, _if_ it's not trapped. But bypassing the checks when it is trapped is > clearly wrong. You can still trap #GP unconditionally and run the emulator. The intercept check will (or should) handle it. Paolo