Re: [PATCH 17/21] KVM: arm64: Use common code's approach for __GFP_ZERO with memory caches

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On 2020-06-11 16:43, Sean Christopherson wrote:
On Thu, Jun 11, 2020 at 08:59:05AM +0100, Marc Zyngier wrote:
>diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>index 9398b66f8a87..688213ef34f0 100644
>--- a/arch/arm64/kvm/mmu.c
>+++ b/arch/arm64/kvm/mmu.c
>@@ -131,7 +131,8 @@ static int mmu_topup_memory_cache(struct
>kvm_mmu_memory_cache *cache, int min)
> 	if (cache->nobjs >= min)
> 		return 0;
> 	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
>-		page = (void *)__get_free_page(GFP_PGTABLE_USER);
>+		page = (void *)__get_free_page(GFP_KERNEL_ACCOUNT |

This is definitely a change in the way we account for guest
page tables allocation, although I find it bizarre that not
all architectures account for it the same way.

It's not intended to be a functional change, i.e. the allocations should
still be accounted:

  #define GFP_PGTABLE_USER  (GFP_PGTABLE_KERNEL | __GFP_ACCOUNT)
  |
  -> #define GFP_PGTABLE_KERNEL        (GFP_KERNEL | __GFP_ZERO)

  == GFP_KERNEL | __GFP_ACCOUNT | __GFP_ZERO

versus

  #define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT)

    with __GFP_ZERO explicitly OR'd in

  == GFP_KERNEL | __GFP_ACCOUNT | __GFP_ZERO

I can put the above in the changelog, unless of course it's wrong and I've
missed something.

Ah, good point. Serves me right for judging the symbol at face value! ;-)
I guess a quick mention in the changelog wouldn't hurt.

Thanks,

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



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