Re: [PATCH v5 12/12] KVM: arm64: Use local TLBI on permission relaxation

[Ricardo Koller <ricarkol@google.com>]

Hi Vladimir,

On Thu, Mar 02, 2023 at 10:45:25AM +0000, Vladimir Murzin wrote:
> On 3/1/23 21:09, Ricardo Koller wrote:
> > Second, KVM does not set the VTTBR_EL2.CnP bit, so each
> > PE has its own TLB entry for the same page. KVM could tolerate that when
> > doing permission relaxation (i.e., not having changes broadcasted to all
> > PEs).
> 
> I'm might be missing something, but it seems that we do set CnP bit, at
> least in v6.2 we have
> 
> arch/arm64/include/asm/kvm_mmu.h
> 
> static __always_inline u64 kvm_get_vttbr(struct kvm_s2_mmu *mmu)
> {
>         struct kvm_vmid *vmid = &mmu->vmid;
>         u64 vmid_field, baddr;
>         u64 cnp = system_supports_cnp() ? VTTBR_CNP_BIT : 0;
> 
>         baddr = mmu->pgd_phys;
>         vmid_field = atomic64_read(&vmid->id) << VTTBR_VMID_SHIFT;
>         vmid_field &= VTTBR_VMID_MASK(kvm_arm_vmid_bits);
>         return kvm_phys_to_vttbr(baddr) | vmid_field | cnp;
> }
> 
> Cheers
> Vladimir

I need to fix the commit message. What I meant to say is that
this optimization is correct in the case where CnP is not set.

Thanks,
Ricardo