Re: [PATCH v3 20/21] KVM: arm64: Remove unused 'pgd' field from 'struct kvm_s2_mmu'

Will Deacon
2020-09-03T16:51:31Z

On Thu, Sep 03, 2020 at 03:07:17PM +1000, Gavin Shan wrote:
> On 8/25/20 7:39 PM, Will Deacon wrote:
> > The stage-2 page-tables are entirely encapsulated by the 'pgt' field of
> > 'struct kvm_s2_mmu', so remove the unused 'pgd' field.
> >
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Quentin Perret <qperret@google.com>
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> > arch/arm64/include/asm/kvm_host.h | 1 -
> > arch/arm64/kvm/mmu.c | 2 --
> > 2 files changed, 3 deletions(-)
> >
>
> I think this might be folded into PATCH[18] as both patches are
> simple enough. I'm not sure the changes introduced in PATCH[19]
> prevent us doing this.
>
> There is another question below.
>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
>
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 0b7c702b2151..41caf29bd93c 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -79,7 +79,6 @@ struct kvm_s2_mmu {
> > * for vEL1/EL0 with vHCR_EL2.VM == 0. In that case, we use the
> > * canonical stage-2 page tables.
> > */
> > - pgd_t *pgd;
> > phys_addr_t pgd_phys;
> > struct kvm_pgtable *pgt;
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index ddeec0b03666..f28e03dcb897 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -384,7 +384,6 @@ int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
> > mmu->kvm = kvm;
> > mmu->pgt = pgt;
> > mmu->pgd_phys = __pa(pgt->pgd);
> > - mmu->pgd = (void *)pgt->pgd;
> > mmu->vmid.vmid_gen = 0;
> > return 0;
> > @@ -470,7 +469,6 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
> > spin_lock(&kvm->mmu_lock);
> > pgt = mmu->pgt;
> > if (pgt) {
> > - mmu->pgd = NULL;
> > mmu->pgd_phys = 0;
> > mmu->pgt = NULL;
> > free_percpu(mmu->last_vcpu_ran);
> >
>
> I guess mmu->pgd_phys might be removed either because kvm_get_vttbr()
> is the only consumer.

Hmm, but kvm_get_vttbr() is still used after these patches, so I think
the pgd_phys field needs to stick around.

Will