linux-kernel - Re: [PATCH v2 1/2] mm/userfaultfd: don't place zeropages when zeropages are disallowed

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Message-ID: <15bb1139-97aa-484c-9087-dccf6612ed39@redhat.com>
Date: Thu, 11 Apr 2024 14:55:12 +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 1/2] mm/userfaultfd: don't place zeropages when
 zeropages are disallowed

On 11.04.24 14:30, David Hildenbrand wrote:
> On 11.04.24 14:26, Alexander Gordeev wrote:
>> On Wed, Mar 27, 2024 at 06:17:36PM +0100, David Hildenbrand wrote:
>>
>> Hi David,
>> ...
>>>    static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
>>>    				     struct vm_area_struct *dst_vma,
>>>    				     unsigned long dst_addr)
>>> @@ -324,6 +355,9 @@ static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
>>>    	spinlock_t *ptl;
>>>    	int ret;
>>>    
>>> +	if (mm_forbids_zeropage(dst_vma->mm))
>>
>> I assume, you were going to pass dst_vma->vm_mm here?
>> This patch does not compile otherwise.
> 
> Ah, I compiled it only on x86, where the parameter is ignored ... and
> for testing the code path I forced mm_forbids_zeropage to be 1 on x86.

Now I get it, I compiled it all on s390x, but not the individual 
patches, so patch #2 hid the issue in patch #1. Sneaky. :)

-- 
Cheers,

David / dhildenb