Re: [PATCH v4 2/9] KVM: x86: MMU: Clear CR3 LAM bits when allocate shadow root

Robert Hoo
2023-02-09T13:03:05Z

On Thu, 2023-02-09 at 17:55 +0800, Chao Gao wrote:
> On Thu, Feb 09, 2023 at 10:40:15AM +0800, Robert Hoo wrote:
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3698,8 +3698,11 @@ static int mmu_alloc_shadow_roots(struct
> > kvm_vcpu *vcpu)
> > gfn_t root_gfn, root_pgd;
> > int quadrant, i, r;
> > hpa_t root;
> > -
>
> The blank line should be kept.

OK
>
> > +#ifdef CONFIG_X86_64
> > + root_pgd = mmu->get_guest_pgd(vcpu) & ~(X86_CR3_LAM_U48 |
> > X86_CR3_LAM_U57);
> > +#else
> > root_pgd = mmu->get_guest_pgd(vcpu);
> > +#endif
>
> Why are other call sites of mmu->get_guest_pgd() not changed?

Emm, the other 3 are
FNAME(walk_addr_generic)()
kvm_arch_setup_async_pf()
kvm_arch_async_page_ready

In former version, I clear CR3.LAM bits for guest_pgd inside mmu-
>get_guest_pgd(). I think this is generic. Perhaps I should still do it
in that way. Let's wait for other's comments on this.
Thanks for pointing out.

> And what's
> the value of the #ifdef?

LAM is only available in 64 bit mode.
>
> > root_gfn = root_pgd >> PAGE_SHIFT;
> >
> > if (mmu_check_root(vcpu, root_gfn))
> > --
> > 2.31.1
> >