linux-kernel - Re: [PATCH 17/21] KVM: arm64: Use common code's approach for __GFP

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Message-ID: <12ec535821111d503773d6f623047d27@kernel.org>
Date:   Thu, 11 Jun 2020 16:51:39 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Peter Feiner <pfeiner@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [PATCH 17/21] KVM: arm64: Use common code's approach for
 __GFP_ZERO with memory caches

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...