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

Marc Zyngier
2020-09-04T10:04:49Z

On 2020-09-04 01:59, Gavin Shan wrote:
> Hi Will,
>
> On 9/4/20 2:50 AM, Will Deacon wrote:
>> 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.
>>
>
> Yes, kvm_get_vttbr() is the only consumer. The corresponding physical
> address can be figured out in the function, we needn't have the
> physical
> address and cache it in advance. However, it's not a big deal. I
> probably
> post one patch to remove it after this series gets merged.
>
> baddr = __pa(mmu->pgt->pgd);

I'd rather you didn't. The NV patches need it for the AT emulation code,
so it might as well stay in place.

Thanks,

M.
--
Jazz is not dead. It just smells funny...