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Message-ID: <90e7b37a614d2cd723726a44b81395c3e9d158f0.camel@redhat.com>
Date: Mon, 05 Oct 2020 16:06:25 +0300
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
Wei Huang <whuang2@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] KVM: x86: disconnect kvm_check_cpuid() from
vcpu->arch.cpuid_entries
On Mon, 2020-10-05 at 13:51 +0200, Vitaly Kuznetsov wrote:
> Maxim Levitsky <mlevitsk@...hat.com> writes:
>
> > On Thu, 2020-10-01 at 15:05 +0200, Vitaly Kuznetsov wrote:
> > > As a preparatory step to allocating vcpu->arch.cpuid_entries dynamically
> > > make kvm_check_cpuid() check work with an arbitrary 'struct kvm_cpuid_entry2'
> > > array.
> > >
> > > Currently, when kvm_check_cpuid() fails we reset vcpu->arch.cpuid_nent to
> > > 0 and this is kind of weird, i.e. one would expect CPUIDs to remain
> > > unchanged when KVM_SET_CPUID[2] call fails.
> > Since this specific patch doesn't fix this, maybe move this chunk to following patches,
> > or to the cover letter?
>
> Basically, this kind of pairs with what's after 'No functional change
> intended' below: we admit the problem but don't fix it because we can't
> (yet) and then in PATCH3 we do two things at once. It would be great to
> separate these two changes but this doesn't seem to be possible without
> an unneeded code churn.
>
> That said, I'm completely fine with dropping this chunk from the commit
> message if it sound inapropriate here.
It just threw me a bit off course while trying to understand what the patch does.
Best regards,
Maxim Levitsky
>
> > > No functional change intended. It would've been possible to move the updated
> > > kvm_check_cpuid() in kvm_vcpu_ioctl_set_cpuid2() and check the supplied
> > > input before we start updating vcpu->arch.cpuid_entries/nent but we
> > > can't do the same in kvm_vcpu_ioctl_set_cpuid() as we'll have to copy
> > > 'struct kvm_cpuid_entry' entries first. The change will be made when
> > > vcpu->arch.cpuid_entries[] array becomes allocated dynamically.
> > >
> > > Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > > Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> > > ---
> > > arch/x86/kvm/cpuid.c | 38 +++++++++++++++++++++++---------------
> > > 1 file changed, 23 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > > index 37c3668a774f..529348ddedc1 100644
> > > --- a/arch/x86/kvm/cpuid.c
> > > +++ b/arch/x86/kvm/cpuid.c
> > > @@ -54,7 +54,24 @@ static u32 xstate_required_size(u64 xstate_bv, bool compacted)
> > >
> > > #define F feature_bit
> > >
> > > -static int kvm_check_cpuid(struct kvm_vcpu *vcpu)
> > > +static inline struct kvm_cpuid_entry2 *cpuid_entry2_find(
> > > + struct kvm_cpuid_entry2 *entries, int nent, u32 function, u32 index)
> > > +{
> > > + struct kvm_cpuid_entry2 *e;
> > > + int i;
> > > +
> > > + for (i = 0; i < nent; i++) {
> > > + e = &entries[i];
> > > +
> > > + if (e->function == function && (e->index == index ||
> > > + !(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX)))
> > > + return e;
> > > + }
> > > +
> > > + return NULL;
> > > +}
> > > +
> > > +static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
> > > {
> > > struct kvm_cpuid_entry2 *best;
> > >
> > > @@ -62,7 +79,7 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu)
> > > * The existing code assumes virtual address is 48-bit or 57-bit in the
> > > * canonical address checks; exit if it is ever changed.
> > > */
> > > - best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
> > > + best = cpuid_entry2_find(entries, nent, 0x80000008, 0);
> > > if (best) {
> > > int vaddr_bits = (best->eax & 0xff00) >> 8;
> > >
> > > @@ -220,7 +237,7 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
> > > vcpu->arch.cpuid_entries[i].padding[2] = 0;
> > > }
> > > vcpu->arch.cpuid_nent = cpuid->nent;
> > > - r = kvm_check_cpuid(vcpu);
> > > + r = kvm_check_cpuid(vcpu->arch.cpuid_entries, cpuid->nent);
> > > if (r) {
> > > vcpu->arch.cpuid_nent = 0;
> > > kvfree(cpuid_entries);
> > > @@ -250,7 +267,7 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
> > > cpuid->nent * sizeof(struct kvm_cpuid_entry2)))
> > > goto out;
> > > vcpu->arch.cpuid_nent = cpuid->nent;
> > > - r = kvm_check_cpuid(vcpu);
> > > + r = kvm_check_cpuid(vcpu->arch.cpuid_entries, cpuid->nent);
> > > if (r) {
> > > vcpu->arch.cpuid_nent = 0;
> > > goto out;
> > > @@ -940,17 +957,8 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
> > > struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
> > > u32 function, u32 index)
> > > {
> > > - struct kvm_cpuid_entry2 *e;
> > > - int i;
> > > -
> > > - for (i = 0; i < vcpu->arch.cpuid_nent; ++i) {
> > > - e = &vcpu->arch.cpuid_entries[i];
> > > -
> > > - if (e->function == function && (e->index == index ||
> > > - !(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX)))
> > > - return e;
> > > - }
> > > - return NULL;
> > > + return cpuid_entry2_find(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent,
> > > + function, index);
> > > }
> > > EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);
> > >
> >
> > Other than minor note to the commit message, this looks fine, so
> > Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> >
>
> Thanks!
>
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