RE: [PATCH v3 11/11] KVM:SVM: Enable INVPCID feature on AMD

Babu Moger
2020-07-30T16:33:08Z

> -----Original Message-----
> From: kvm-owner@vger.kernel.org <kvm-owner@vger.kernel.org> On Behalf
> Of Jim Mattson
> Sent: Wednesday, July 29, 2020 6:01 PM
> To: Moger, Babu <Babu.Moger@amd.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>; Vitaly Kuznetsov
> <vkuznets@redhat.com>; Wanpeng Li <wanpengli@tencent.com>; Sean
> Christopherson <sean.j.christopherson@intel.com>; kvm list
> <kvm@vger.kernel.org>; Joerg Roedel <joro@8bytes.org>; the arch/x86
> maintainers <x86@kernel.org>; LKML <linux-kernel@vger.kernel.org>; Ingo
> Molnar <mingo@redhat.com>; Borislav Petkov <bp@alien8.de>; H . Peter Anvin
> <hpa@zytor.com>; Thomas Gleixner <tglx@linutronix.de>
> Subject: Re: [PATCH v3 11/11] KVM:SVM: Enable INVPCID feature on AMD
>
> On Tue, Jul 28, 2020 at 4:39 PM Babu Moger <babu.moger@amd.com> wrote:
> >
> > The following intercept bit has been added to support VMEXIT for
> > INVPCID instruction:
> > Code Name Cause
> > A2h VMEXIT_INVPCID INVPCID instruction
> >
> > The following bit has been added to the VMCB layout control area to
> > control intercept of INVPCID:
> > Byte Offset Bit(s) Function
> > 14h 2 intercept INVPCID
> >
> > Enable the interceptions when the the guest is running with shadow
> > page table enabled and handle the tlbflush based on the invpcid
> > instruction type.
> >
> > For the guests with nested page table (NPT) support, the INVPCID
> > feature works as running it natively. KVM does not need to do any
> > special handling in this case.
> >
> > AMD documentation for INVPCID feature is available at "AMD64
> > Architecture Programmer’s Manual Volume 2: System Programming, Pub.
> > 24593 Rev. 3.34(or later)"
> >
> > The documentation can be obtained at the links below:
> > Link:
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.
> >
> amd.com%2Fsystem%2Ffiles%2FTechDocs%2F24593.pdf&amp;data=02%7C01%
> 7CBab
> >
> u.Moger%40amd.com%7C68f9bafe44704700ac3b08d834135678%7C3dd8961fe
> 4884e6
> >
> 08e11a82d994e183d%7C0%7C0%7C637316605732430961&amp;sdata=c%2Fss1
> 2Y5Hcy
> > pwDfEIv8kHiI33XI6jtLAb5wUm96%2BY8I%3D&amp;reserved=0
> > Link:
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugz
> >
> illa.kernel.org%2Fshow_bug.cgi%3Fid%3D206537&amp;data=02%7C01%7CBab
> u.M
> >
> oger%40amd.com%7C68f9bafe44704700ac3b08d834135678%7C3dd8961fe488
> 4e608e
> >
> 11a82d994e183d%7C0%7C0%7C637316605732430961&amp;sdata=wv5px6rzaT
> R8DcZl
> > CWpAkAFMkAv61XkdRv3274BJD6A%3D&amp;reserved=0
> >
> > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > ---
> > arch/x86/include/uapi/asm/svm.h | 2 +
> > arch/x86/kvm/svm/svm.c | 64
> +++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 66 insertions(+)
> >
> > diff --git a/arch/x86/include/uapi/asm/svm.h
> > b/arch/x86/include/uapi/asm/svm.h index 2e8a30f06c74..522d42dfc28c
> > 100644
> > --- a/arch/x86/include/uapi/asm/svm.h
> > +++ b/arch/x86/include/uapi/asm/svm.h
> > @@ -76,6 +76,7 @@
> > #define SVM_EXIT_MWAIT_COND 0x08c
> > #define SVM_EXIT_XSETBV 0x08d
> > #define SVM_EXIT_RDPRU 0x08e
> > +#define SVM_EXIT_INVPCID 0x0a2
> > #define SVM_EXIT_NPF 0x400
> > #define SVM_EXIT_AVIC_INCOMPLETE_IPI 0x401
> > #define SVM_EXIT_AVIC_UNACCELERATED_ACCESS 0x402
> > @@ -171,6 +172,7 @@
> > { SVM_EXIT_MONITOR, "monitor" }, \
> > { SVM_EXIT_MWAIT, "mwait" }, \
> > { SVM_EXIT_XSETBV, "xsetbv" }, \
> > + { SVM_EXIT_INVPCID, "invpcid" }, \
> > { SVM_EXIT_NPF, "npf" }, \
> > { SVM_EXIT_AVIC_INCOMPLETE_IPI, "avic_incomplete_ipi" }, \
> > { SVM_EXIT_AVIC_UNACCELERATED_ACCESS,
> "avic_unaccelerated_access" }, \
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index
> > 99cc9c285fe6..6b099e0b28c0 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -813,6 +813,11 @@ static __init void svm_set_cpu_caps(void)
> > if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
> > boot_cpu_has(X86_FEATURE_AMD_SSBD))
> > kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
> > +
> > + /* Enable INVPCID if both PCID and INVPCID enabled */
> > + if (boot_cpu_has(X86_FEATURE_PCID) &&
> > + boot_cpu_has(X86_FEATURE_INVPCID))
> > + kvm_cpu_cap_set(X86_FEATURE_INVPCID);
> > }
>
> Why is PCID required? Can't this just be
> 'kvm_cpu_cap_check_and_set(X86_FEATURE_INVPCID);'?

Ok. Let me check.
>
> > static __init int svm_hardware_setup(void) @@ -1099,6 +1104,18 @@
> > static void init_vmcb(struct vcpu_svm *svm)
> > clr_intercept(svm, INTERCEPT_PAUSE);
> > }
> >
> > + /*
> > + * Intercept INVPCID instruction only if shadow page table is
> > + * enabled. Interception is not required with nested page table
> > + * enabled.
> > + */
> > + if (boot_cpu_has(X86_FEATURE_INVPCID)) {
>
> Shouldn't this be 'kvm_cpu_cap_has(X86_FEATURE_INVPCID),' so that it is
> consistent with the code above?

Sure. Will check on it.

>
> > + if (!npt_enabled)
> > + set_intercept(svm, INTERCEPT_INVPCID);
> > + else
> > + clr_intercept(svm, INTERCEPT_INVPCID);
> > + }
> > +
> > if (kvm_vcpu_apicv_active(&svm->vcpu))
> > avic_init_vmcb(svm);
> >
> > @@ -2715,6 +2732,43 @@ static int mwait_interception(struct vcpu_svm
> *svm)
> > return nop_interception(svm);
> > }
> >
> > +static int invpcid_interception(struct vcpu_svm *svm) {
> > + struct kvm_vcpu *vcpu = &svm->vcpu;
> > + struct x86_exception e;
> > + unsigned long type;
> > + gva_t gva;
> > + struct {
> > + u64 pcid;
> > + u64 gla;
> > + } operand;
> > +
> > + if (!guest_cpuid_has(vcpu, X86_FEATURE_INVPCID)) {
> > + kvm_queue_exception(vcpu, UD_VECTOR);
> > + return 1;
> > + }
> > +
> > + /*
> > + * For an INVPCID intercept:
> > + * EXITINFO1 provides the linear address of the memory operand.
> > + * EXITINFO2 provides the contents of the register operand.
> > + */
> > + type = svm->vmcb->control.exit_info_2;
> > + gva = svm->vmcb->control.exit_info_1;
> > +
> > + if (type > 3) {
> > + kvm_inject_gp(vcpu, 0);
> > + return 1;
> > + }
> > +
> > + if (kvm_read_guest_virt(vcpu, gva, &operand, sizeof(operand), &e)) {
> > + kvm_inject_emulated_page_fault(vcpu, &e);
> > + return 1;
> > + }
>
> The emulated page fault is not always correct. See commit
> 7a35e515a7055 ("KVM: VMX: Properly handle kvm_read/write_guest_virt*()
> result"). I don't think the problems are only on the VMX side.

Ok. Sure. Will take a look.

>
> > +
> > + return kvm_handle_invpcid(vcpu, type, operand.pcid,
> > +operand.gla); }
> > +
> > static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
> > [SVM_EXIT_READ_CR0] = cr_interception,
> > [SVM_EXIT_READ_CR3] = cr_interception,
> > @@ -2777,6 +2831,7 @@ static int (*const svm_exit_handlers[])(struct
> vcpu_svm *svm) = {
> > [SVM_EXIT_MWAIT] = mwait_interception,
> > [SVM_EXIT_XSETBV] = xsetbv_interception,
> > [SVM_EXIT_RDPRU] = rdpru_interception,
> > + [SVM_EXIT_INVPCID] = invpcid_interception,
> > [SVM_EXIT_NPF] = npf_interception,
> > [SVM_EXIT_RSM] = rsm_interception,
> > [SVM_EXIT_AVIC_INCOMPLETE_IPI] =
> avic_incomplete_ipi_interception,
> > @@ -3562,6 +3617,15 @@ static void svm_cpuid_update(struct kvm_vcpu
> *vcpu)
> > svm->nrips_enabled = kvm_cpu_cap_has(X86_FEATURE_NRIPS) &&
> > guest_cpuid_has(&svm->vcpu,
> > X86_FEATURE_NRIPS);
> >
> > + /* Check again if INVPCID interception if required */
> > + if (boot_cpu_has(X86_FEATURE_INVPCID) &&
>
> Again, shouldn't this be 'kvm_cpu_cap_has(X86_FEATURE_INVPCID)'?
> (Better, perhaps, would be to extract this common block of code into a separate
> function to be called from both places.)

Sure. Will work on it.
Thanks
>
> > + guest_cpuid_has(vcpu, X86_FEATURE_INVPCID)) {
> > + if (!npt_enabled)
> > + set_intercept(svm, INTERCEPT_INVPCID);
> > + else
> > + clr_intercept(svm, INTERCEPT_INVPCID);
> > + }
> > +
> > if (!kvm_vcpu_apicv_active(vcpu))
> > return;
> >
> >