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Date: Fri, 12 Jun 2020 16:47:46 -0500
From: Babu Moger <babu.moger@....com>
To: Jim Mattson <jmattson@...gle.com>
Cc: Wanpeng Li <wanpengli@...cent.com>, Joerg Roedel <joro@...tes.org>,
the arch/x86 maintainers <x86@...nel.org>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H . Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] KVM:SVM: Enable INVPCID feature on AMD
On 6/12/20 3:10 PM, Jim Mattson wrote:
> On Fri, Jun 12, 2020 at 12:35 PM Babu Moger <babu.moger@....com> wrote:
>>
>>
>>
>>> -----Original Message-----
>>> From: Jim Mattson <jmattson@...gle.com>
>>> Sent: Thursday, June 11, 2020 6:51 PM
>>> To: Moger, Babu <Babu.Moger@....com>
>>> Cc: Wanpeng Li <wanpengli@...cent.com>; Joerg Roedel <joro@...tes.org>;
>>> the arch/x86 maintainers <x86@...nel.org>; Sean Christopherson
>>> <sean.j.christopherson@...el.com>; Ingo Molnar <mingo@...hat.com>;
>>> Borislav Petkov <bp@...en8.de>; H . Peter Anvin <hpa@...or.com>; Paolo
>>> Bonzini <pbonzini@...hat.com>; Vitaly Kuznetsov <vkuznets@...hat.com>;
>>> Thomas Gleixner <tglx@...utronix.de>; LKML <linux-kernel@...r.kernel.org>;
>>> kvm list <kvm@...r.kernel.org>
>>> Subject: Re: [PATCH 3/3] KVM:SVM: Enable INVPCID feature on AMD
>>>
>>> On Thu, Jun 11, 2020 at 2:48 PM Babu Moger <babu.moger@....com> wrote:
>>>>
>>>> The following intercept is added for INVPCID instruction:
>>>> Code Name Cause
>>>> A2h VMEXIT_INVPCID INVPCID instruction
>>>>
>>>> The following bit is added to the VMCB layout control area
>>>> to control intercept of INVPCID:
>>>> Byte Offset Bit(s) Function
>>>> 14h 2 intercept INVPCID
>>>>
>>>> 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.
>>>>
>>>> Interceptions are required in the following cases.
>>>> 1. If the guest tries to disable the feature when the underlying
>>>> hardware supports it. In this case hypervisor needs to report #UD.
>>>
>>> Per the AMD documentation, attempts to use INVPCID at CPL>0 will
>>> result in a #GP, regardless of the intercept bit. If the guest CPUID
>>> doesn't enumerate the feature, shouldn't the instruction raise #UD
>>> regardless of CPL? This seems to imply that we should intercept #GP
>>> and decode the instruction to see if we should synthesize #UD instead.
>>
>> Purpose here is to report UD when the guest CPUID doesn't enumerate the
>> INVPCID feature When Bare-metal supports it. It seems to work fine for
>> that purpose. You are right. The #GP for CPL>0 takes precedence over
>> interception. No. I am not planning to intercept GP.
>
> WIthout intercepting #GP, you fail to achieve your stated purpose.
I think I have misunderstood this part. I was not inteding to change the
#GP behaviour. I will remove this part. My intension of these series is to
handle invpcid in shadow page mode. I have verified that part. Hope I did
not miss anything else.
>
>> I will change the text. How about this?
>>
>> Interceptions are required in the following cases.
>> 1. If the guest CPUID doesn't enumerate the INVPCID feature when the
>> underlying hardware supports it, hypervisor needs to report UD. However,
>> #GP for CPL>0 takes precedence over interception.
>
> This text is not internally consistent. In one sentence, you say that
> "hypervisor needs to report #UD." In the next sentence, you are
> essentially saying that the hypervisor doesn't need to report #UD.
> Which is it?
>
>>>> 2. When the guest is running with shadow page table enabled, in
>>>> this case the hypervisor needs to handle the tlbflush based on the
>>>> type of invpcid instruction type.
>>>>
>>>> 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.a
>>> md.com%2Fsystem%2Ffiles%2FTechDocs%2F24593.pdf&data=02%7C01%7
>>> Cbabu.moger%40amd.com%7C36861b25f6d143e3b38e08d80e624472%7C3dd8
>>> 961fe4884e608e11a82d994e183d%7C0%7C0%7C637275163374103811&s
>>> data=E%2Fdb6T%2BdO4nrtUoqhKidF6XyorsWrphj6O4WwNZpmYA%3D&res
>>> erved=0
>>>> Link:
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.
>>> kernel.org%2Fshow_bug.cgi%3Fid%3D206537&data=02%7C01%7Cbabu.m
>>> oger%40amd.com%7C36861b25f6d143e3b38e08d80e624472%7C3dd8961fe488
>>> 4e608e11a82d994e183d%7C0%7C0%7C637275163374103811&sdata=b81
>>> 9W%2FhKS93%2BAp3QvcsR0BwTQpUVUFMbIaNaisgWHRY%3D&reserved=
>>> 0
>>>>
>>>> Signed-off-by: Babu Moger <babu.moger@....com>
>>>> ---
>>>> arch/x86/include/asm/svm.h | 4 ++++
>>>> arch/x86/include/uapi/asm/svm.h | 2 ++
>>>> arch/x86/kvm/svm/svm.c | 42
>>> +++++++++++++++++++++++++++++++++++++++
>>>> 3 files changed, 48 insertions(+)
>>>>
>>>> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
>>>> index 62649fba8908..6488094f67fa 100644
>>>> --- a/arch/x86/include/asm/svm.h
>>>> +++ b/arch/x86/include/asm/svm.h
>>>> @@ -55,6 +55,10 @@ enum {
>>>> INTERCEPT_RDPRU,
>>>> };
>>>>
>>>> +/* Extended Intercept bits */
>>>> +enum {
>>>> + INTERCEPT_INVPCID = 2,
>>>> +};
>>>>
>>>> struct __attribute__ ((__packed__)) vmcb_control_area {
>>>> u32 intercept_cr;
>>>> 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 285e5e1ff518..82d974338f68 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);
>>>> }
>>>>
>>>> static __init int svm_hardware_setup(void)
>>>> @@ -1099,6 +1104,17 @@ 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.
>>>> + */
>>>> + if (boot_cpu_has(X86_FEATURE_INVPCID)) {
>>>> + if (!npt_enabled)
>>>> + set_extended_intercept(svm, INTERCEPT_INVPCID);
>>>> + else
>>>> + clr_extended_intercept(svm, INTERCEPT_INVPCID);
>>>> + }
>>>> +
>>>> if (kvm_vcpu_apicv_active(&svm->vcpu))
>>>> avic_init_vmcb(svm);
>>>>
>>>> @@ -2715,6 +2731,23 @@ 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;
>>>> + unsigned long type;
>>>> + gva_t gva;
>>>> +
>>>> + /*
>>>> + * 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;
>>>> +
>>>> + return kvm_handle_invpcid_types(vcpu, gva, type);
>>>> +}
>>>> +
>>>> static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
>>>> [SVM_EXIT_READ_CR0] = cr_interception,
>>>> [SVM_EXIT_READ_CR3] = cr_interception,
>>>> @@ -2777,6 +2810,7 @@ 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 +3596,14 @@ 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);
>>>>
>>>> + /*
>>>> + * Intercept INVPCID instruction if the baremetal has the support
>>>> + * but the guest doesn't claim the feature.
>>>> + */
>>>> + if (boot_cpu_has(X86_FEATURE_INVPCID) &&
>>>> + !guest_cpuid_has(vcpu, X86_FEATURE_INVPCID))
>>>> + set_extended_intercept(svm, INTERCEPT_INVPCID);
>>>> +
>>>
>>> What if INVPCID is enabled in the guest CPUID later? Shouldn't we then
>>> clear this intercept bit?
>>
>> I assume the feature enable comes in the same code path as this. I can add
>> "if else" check here if that is what you are suggesting.
>
> Yes, that's what I'm suggesting.
>
>>>
>>>> if (!kvm_vcpu_apicv_active(vcpu))
>>>> return;
>>>>
>>>>
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