linux-kernel - Re: [PATCH] KVM: VMX: Add a wrapper for reading INVPCID/INVEPT/INVVPID type

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Date:   Thu, 14 Oct 2021 16:54:30 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Vipin Sharma <vipinsh@...gle.com>, pbonzini@...hat.com,
        dmatlack@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: Add a wrapper for reading
 INVPCID/INVEPT/INVVPID type

On Mon, Oct 11, 2021, Jim Mattson wrote:
> On Mon, Oct 11, 2021 at 1:23 PM Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > On Mon, Oct 11, 2021, Vipin Sharma wrote:
> > > -     if (type > 3) {
> > > +     if (type > INVPCID_TYPE_MAX) {
> >
> > Hrm, I don't love this because it's not auto-updating in the unlikely chance that
> > a new type is added.  I definitely don't like open coding '3' either.  What about
> > going with a verbose option of
> >
> >         if (type != INVPCID_TYPE_INDIV_ADDR &&
> >             type != INVPCID_TYPE_SINGLE_CTXT &&
> >             type != INVPCID_TYPE_ALL_INCL_GLOBAL &&
> >             type != INVPCID_TYPE_ALL_NON_GLOBAL) {
> >                 kvm_inject_gp(vcpu, 0);
> >                 return 1;
> >         }
> 
> Better, perhaps, to introduce a new function, valid_invpcid_type(),
> and squirrel away the ugliness there?

Oh, yeah, definitely.  I missed that SVM's invpcid_interception() has the same
open-coded check.

Alternatively, could we handle the invalid type in the main switch statement?  I
don't see anything in the SDM or APM that architecturally _requires_ the type be
checked before reading the INVPCID descriptor.  Hardware may operate that way,
but that's uArch specific behavior unless there's explicit documentation.


diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 89077160d463..c8aade2e2a20 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3119,11 +3119,6 @@ static int invpcid_interception(struct kvm_vcpu *vcpu)
        type = svm->vmcb->control.exit_info_2;
        gva = svm->vmcb->control.exit_info_1;

-       if (type > 3) {
-               kvm_inject_gp(vcpu, 0);
-               return 1;
-       }
-
        return kvm_handle_invpcid(vcpu, type, gva);
 }

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1c8b2b6e7ed9..ad2e794d4cb2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5504,11 +5504,6 @@ static int handle_invpcid(struct kvm_vcpu *vcpu)
        vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
        type = kvm_register_read(vcpu, (vmx_instruction_info >> 28) & 0xf);

-       if (type > 3) {
-               kvm_inject_gp(vcpu, 0);
-               return 1;
-       }
-
        /* According to the Intel instruction reference, the memory operand
         * is read even if it isn't needed (e.g., for type==all)
         */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d9273f536f9d..a3657db6daf9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12382,7 +12382,8 @@ int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva)
                return kvm_skip_emulated_instruction(vcpu);

        default:
-               BUG(); /* We have already checked above that type <= 3 */
+               kvm_inject_gp(vcpu, 0);
+               return 1;
        }
 }
 EXPORT_SYMBOL_GPL(kvm_handle_invpcid);