linux-kernel - Re: [PATCH v1 1/9] mm/memory: factor out zapping of present pte into zap_present

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Date: Tue, 30 Jan 2024 09:49:00 +0100
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
 Nick Piggin <npiggin@...il.com>, Peter Zijlstra <peterz@...radead.org>,
 Michael Ellerman <mpe@...erman.id.au>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Arnd Bergmann <arnd@...db.de>,
 linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-s390@...r.kernel.org
Subject: Re: [PATCH v1 1/9] mm/memory: factor out zapping of present pte into
 zap_present_pte()

On 30.01.24 09:46, Ryan Roberts wrote:
> On 30/01/2024 08:41, David Hildenbrand wrote:
>> On 30.01.24 09:13, Ryan Roberts wrote:
>>> On 29/01/2024 14:32, David Hildenbrand wrote:
>>>> Let's prepare for further changes by factoring out processing of present
>>>> PTEs.
>>>>
>>>> Signed-off-by: David Hildenbrand <david@...hat.com>
>>>> ---
>>>>    mm/memory.c | 92 ++++++++++++++++++++++++++++++-----------------------
>>>>    1 file changed, 52 insertions(+), 40 deletions(-)
>>>>
>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>> index b05fd28dbce1..50a6c79c78fc 100644
>>>> --- a/mm/memory.c
>>>> +++ b/mm/memory.c
>>>> @@ -1532,13 +1532,61 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct
>>>> *vma,
>>>>        pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
>>>>    }
>>>>    +static inline void zap_present_pte(struct mmu_gather *tlb,
>>>> +        struct vm_area_struct *vma, pte_t *pte, pte_t ptent,
>>>> +        unsigned long addr, struct zap_details *details,
>>>> +        int *rss, bool *force_flush, bool *force_break)
>>>> +{
>>>> +    struct mm_struct *mm = tlb->mm;
>>>> +    bool delay_rmap = false;
>>>> +    struct folio *folio;
>>>
>>> You need to init this to NULL otherwise its a random value when calling
>>> should_zap_folio() if vm_normal_page() returns NULL.
>>
>> Right, and we can stop setting it to NULL in the original function. Patch #2
>> changes these checks, which is why it's only a problem in this patch.
> 
> Yeah I only noticed that after sending out this reply and moving to the next
> patch. Still worth fixing this intermediate state I think.

Absolutely, I didn't do path-by-patch compilation yet (I suspect the 
compiler would complain).

-- 
Cheers,

David / dhildenb