Re: [PATCH v2 5/9] KVM: x86/mmu: Factor out the meat of reset_tdp_shadow_zero_bits_mask

Ben Gardon
2022-04-21T18:50:55Z

On Tue, Apr 12, 2022 at 8:46 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Mon, Mar 21, 2022, Ben Gardon wrote:
> > Factor out the implementation of reset_tdp_shadow_zero_bits_mask to a
> > helper function which does not require a vCPU pointer. The only element
> > of the struct kvm_mmu context used by the function is the shadow root
> > level, so pass that in too instead of the mmu context.
> >
> > No functional change intended.
> >
> > Signed-off-by: Ben Gardon <bgardon@google.com>
> > ---
> > arch/x86/kvm/mmu/mmu.c | 17 +++++++++++------
> > 1 file changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 3b8da8b0745e..6f98111f8f8b 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4487,16 +4487,14 @@ static inline bool boot_cpu_is_amd(void)
> > * possible, however, kvm currently does not do execution-protection.
> > */
> > static void
>
> Strongly prefer the newline here get dropped (see below).
>
> > -reset_tdp_shadow_zero_bits_mask(struct kvm_mmu *context)
> > +build_tdp_shadow_zero_bits_mask(struct rsvd_bits_validate *shadow_zero_check,
>
> Kind of a nit, but KVM uses "calc" for this sort of thing. There are no other
> instances of "build_" to describe this behavior.
>
> Am I alone in think that shadow_zero_check is an awful, awful name? E.g. the EPT
> memtype case has legal non-zero values. Anyone object to opportunistically
> renaming the function and the local shadow_zero_check to "rsvd_bits" to shorten
> line lengths and move KVM one step closer to consistent naming?

That makes sense to me. I'm happy to add a commit to this series to
standardize on rsvd_bits.

>
> > + int shadow_root_level)
> > {
> > - struct rsvd_bits_validate *shadow_zero_check;
> > int i;
> >
> > - shadow_zero_check = &context->shadow_zero_check;
> > -
> > if (boot_cpu_is_amd())
> > __reset_rsvds_bits_mask(shadow_zero_check, reserved_hpa_bits(),
> > - context->shadow_root_level, false,
> > + shadow_root_level, false,
> > boot_cpu_has(X86_FEATURE_GBPAGES),
> > false, true);
> > else
> > @@ -4507,12 +4505,19 @@ reset_tdp_shadow_zero_bits_mask(struct kvm_mmu *context)
> > if (!shadow_me_mask)
> > return;
> >
> > - for (i = context->shadow_root_level; --i >= 0;) {
> > + for (i = shadow_root_level; --i >= 0;) {
> > shadow_zero_check->rsvd_bits_mask[0][i] &= ~shadow_me_mask;
> > shadow_zero_check->rsvd_bits_mask[1][i] &= ~shadow_me_mask;
> > }
> > }
> >
> > +static void
> > +reset_tdp_shadow_zero_bits_mask(struct kvm_mmu *context)
>
> One line! Aside from being against the One True Style[*], there is zero reason
> for a newline here.
>
> And I vote to drop the "mask", because (a) it's not a singular mask and (b) it's
> not even a mask in all cases.
>
> And while I'm on a naming consistency rant, s/context/mmu.
>
> I.e. end up with:
>
> static void calc_tdp_shadow_rsvd_bits(struct rsvd_bits_validate *rsvd_bits,
> int shadow_root_level)
>
> static void reset_tdp_shadow_rsvd_bits(struct kvm_mmu *mmu)
>
> [*] https://lore.kernel.org/mm-commits/CAHk-=wjS-Jg7sGMwUPpDsjv392nDOOs0CtUtVkp=S6Q7JzFJRw@mail.gmail.com
>
> > +{
> > + build_tdp_shadow_zero_bits_mask(&context->shadow_zero_check,
> > + context->shadow_root_level);
> > +}
> > +
> > /*
> > * as the comments in reset_shadow_zero_bits_mask() except it
> > * is the shadow page table for intel nested guest.
> > --
> > 2.35.1.894.gb6a874cedc-goog
> >