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Tue, 13 Aug 2019 07:35:29 -0700 (PDT) Subject: Re: [RFC PATCH v6 75/92] kvm: x86: disable gpa_available optimization in emulator_read_write_onepage() To: =?UTF-8?Q?Adalbert_Laz=c4=83r?= , kvm@vger.kernel.org Cc: linux-mm@kvack.org, virtualization@lists.linux-foundation.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Konrad Rzeszutek Wilk , Tamas K Lengyel , Mathieu Tarral , =?UTF-8?Q?Samuel_Laur=c3=a9n?= , Patrick Colp , Jan Kiszka , Stefan Hajnoczi , Weijiang Yang , Yu C Zhang , =?UTF-8?Q?Mihai_Don=c8=9bu?= References: <20190809160047.8319-1-alazar@bitdefender.com> <20190809160047.8319-76-alazar@bitdefender.com> <5d52ca22.1c69fb81.4ceb8.e90bSMTPIN_ADDED_BROKEN@mx.google.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <5b6f78ca-a5c5-80c4-05af-cbf7fabb96b3@redhat.com> Date: Tue, 13 Aug 2019 16:35:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <5d52ca22.1c69fb81.4ceb8.e90bSMTPIN_ADDED_BROKEN@mx.google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 13/08/19 16:33, Adalbert Laz=C4=83r wrote: > On Tue, 13 Aug 2019 10:47:34 +0200, Paolo Bonzini = wrote: >> On 09/08/19 18:00, Adalbert Laz=C4=83r wrote: >>> If the EPT violation was caused by an execute restriction imposed by = the >>> introspection tool, gpa_available will point to the instruction point= er, >>> not the to the read/write location that has to be used to emulate the >>> current instruction. >>> >>> This optimization should be disabled only when the VM is introspected= , >>> not just because the introspection subsystem is present. >>> >>> Signed-off-by: Adalbert Laz=C4=83r >> >> The right thing to do is to not set gpa_available for fetch failures i= n=20 >> kvm_mmu_page_fault instead: >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 24843cf49579..1bdca40fa831 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -5364,8 +5364,12 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, g= va_t cr2, u64 error_code, >> enum emulation_result er; >> bool direct =3D vcpu->arch.mmu->direct_map; >> =20 >> - /* With shadow page tables, fault_address contains a GVA or nGPA. *= / >> - if (vcpu->arch.mmu->direct_map) { >> + /* >> + * With shadow page tables, fault_address contains a GVA or nGPA. >> + * On a fetch fault, fault_address contains the instruction pointer. >> + */ >> + if (vcpu->arch.mmu->direct_map && >> + likely(!(error_code & PFERR_FETCH_MASK)) { >> vcpu->arch.gpa_available =3D true; >> vcpu->arch.gpa_val =3D cr2; >> } > > Sure, but I think we'll have to extend the check. >=20 > Searching the logs I've found: >=20 > kvm/x86: re-translate broken translation that caused EPT violation > =20 > Signed-off-by: Mircea Cirjaliu >=20 > arch/x86/kvm/x86.c | 1 + > 1 file changed, 1 insertion(+) >=20 > /home/b/kvmi@9cad844~1/arch/x86/kvm/x86.c:4757,4762 - /home/b/kvmi@9cad= 844/arch/x86/kvm/x86.c:4757,4763 > */ > if (vcpu->arch.gpa_available && > emulator_can_use_gpa(ctxt) && > + (vcpu->arch.error_code & PFERR_GUEST_FINAL_MASK) && > (addr & ~PAGE_MASK) =3D=3D (vcpu->arch.gpa_val & ~PAGE_MASK)) { > gpa =3D vcpu->arch.gpa_val; > ret =3D vcpu_is_mmio_gpa(vcpu, addr, gpa, write); >=20 Yes, adding that check makes sense as well (still in kvm_mmu_page_fault). Paolo