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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id x81sm2016034wmb.11.2020.10.20.03.34.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Oct 2020 03:34:47 -0700 (PDT) Subject: Re: [PATCH] KVM: VMX: Forbid userspace MSR filters for x2APIC To: Alexander Graf Cc: "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , Aaron Lewis , Peter Xu , Sean Christopherson References: <20201019170519.1855564-1-pbonzini@redhat.com> <618E2129-7AB5-4F0D-A6C9-E782937FE935@amazon.de> From: Paolo Bonzini Message-ID: <6edd5e08-92c2-40ff-57be-37b92d1ca2bc@redhat.com> Date: Tue, 20 Oct 2020 12:34:46 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 20/10/20 11:48, Alexander Graf wrote: > >     count: 1, >     default_allow: false, >     ranges: [ >         { >             flags: KVM_MSR_FILTER_READ, >             nmsrs: 1, >             base: MSR_EFER, >             bitmap: { 1 }, >         }, >     ], > } > > That filter would set all x2apic registers to "deny", but would not be > caught by the code above. Conversely, a range that explicitly allows > x2apic ranges with default_allow=0 would be rejected by this patch. Yes, but the idea is that x2apic registers are always allowed, even overriding default_allow, and therefore it makes no sense to have them in a range. The patch is only making things fail early for userspace, the policy is defined by Sean's patch. Paolo