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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id z4sm10212616wrs.56.2021.06.21.09.39.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jun 2021 09:39:44 -0700 (PDT) Subject: Re: [PATCH] KVM: VMX: Skip #PF(RSVD) intercepts when emulating smaller maxphyaddr To: Jim Mattson , kvm@vger.kernel.org References: <20210618235941.1041604-1-jmattson@google.com> From: Paolo Bonzini Message-ID: <0489dfe0-f897-16fb-c7e6-f419a47a6c31@redhat.com> Date: Mon, 21 Jun 2021 18:39:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210618235941.1041604-1-jmattson@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 19/06/21 01:59, Jim Mattson wrote: > As part of smaller maxphyaddr emulation, kvm needs to intercept > present page faults to see if it needs to add the RSVD flag (bit 3) to > the error code. However, there is no need to intercept page faults > that already have the RSVD flag set. When setting up the page fault > intercept, add the RSVD flag into the #PF error code mask field (but > not the #PF error code match field) to skip the intercept when the > RSVD flag is already set. > > Signed-off-by: Jim Mattson > --- > arch/x86/kvm/vmx/vmx.c | 23 ++++++++++++++--------- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 68a72c80bd3f..1fc28d8b72c7 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -747,16 +747,21 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu) > if (is_guest_mode(vcpu)) > eb |= get_vmcs12(vcpu)->exception_bitmap; > else { > - /* > - * If EPT is enabled, #PF is only trapped if MAXPHYADDR is mismatched > - * between guest and host. In that case we only care about present > - * faults. For vmcs02, however, PFEC_MASK and PFEC_MATCH are set in > - * prepare_vmcs02_rare. > - */ > - bool selective_pf_trap = enable_ept && (eb & (1u << PF_VECTOR)); > - int mask = selective_pf_trap ? PFERR_PRESENT_MASK : 0; > + int mask = 0, match = 0; > + > + if (enable_ept && (eb & (1u << PF_VECTOR))) { > + /* > + * If EPT is enabled, #PF is currently only intercepted > + * if MAXPHYADDR is smaller on the guest than on the > + * host. In that case we only care about present, > + * non-reserved faults. For vmcs02, however, PFEC_MASK > + * and PFEC_MATCH are set in prepare_vmcs02_rare. > + */ > + mask = PFERR_PRESENT_MASK | PFERR_RSVD_MASK; > + match = PFERR_PRESENT_MASK; > + } > vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, mask); > - vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, mask); > + vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, match); > } > > vmcs_write32(EXCEPTION_BITMAP, eb); > Queued, thanks. Paolo