linux-kernel - Re: [PATCH v2 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

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Message-ID: <329758ca-c795-43a3-9788-d83c09247dce@redhat.com>
Date: Thu, 11 Apr 2024 14:48:19 +0200
From: David Hildenbrand <david@...hat.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>, Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Andrea Arcangeli <aarcange@...hat.com>, kvm@...r.kernel.org,
 linux-s390@...r.kernel.org
Subject: Re: [PATCH v2 2/2] s390/mm: re-enable the shared zeropage for !PV and
 !skeys KVM guests

On 11.04.24 14:33, Alexander Gordeev wrote:
> On Wed, Mar 27, 2024 at 06:17:37PM +0100, David Hildenbrand wrote:
>> index 60950e7a25f5..1a71cb19c089 100644
>> --- a/arch/s390/include/asm/pgtable.h
>> +++ b/arch/s390/include/asm/pgtable.h
>> @@ -566,10 +566,19 @@ static inline pud_t set_pud_bit(pud_t pud, pgprot_t prot)
>>   }
>>   
>>   /*
>> - * In the case that a guest uses storage keys
>> - * faults should no longer be backed by zero pages
>> + * As soon as the guest uses storage keys or enables PV, we deduplicate all
>> + * mapped shared zeropages and prevent new shared zeropages from getting
>> + * mapped.
>>    */
>> -#define mm_forbids_zeropage mm_has_pgste
> 
> Should it be the below insted?
> 
> #define mm_forbids_zeropage mm_forbids_zeropage
> 
> Once I add it, it fails to compile, due to the issue in patch #1.

I guess yes. So we tested the unsharing part (why I was seeing unsharing 
triggering), but would have allowed zeropages afterwards. Sight.

Let me retest and resend. Thanks!

-- 
Cheers,

David / dhildenb