linux-kernel - Re: [PATCH 05/19] mm/gup: Detect huge pfnmap entries in gup-fast

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Message-ID: <67d734e4-86ea-462b-b389-6dc14c0b66f9@redhat.com>
Date: Fri, 9 Aug 2024 18:23:53 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>,
 Oscar Salvador <osalvador@...e.de>, Jason Gunthorpe <jgg@...dia.com>,
 Axel Rasmussen <axelrasmussen@...gle.com>,
 linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
 Will Deacon <will@...nel.org>, Gavin Shan <gshan@...hat.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Zi Yan <ziy@...dia.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Catalin Marinas <catalin.marinas@....com>, Ingo Molnar <mingo@...hat.com>,
 Alistair Popple <apopple@...dia.com>, Borislav Petkov <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Alex Williamson <alex.williamson@...hat.com>, Yan Zhao <yan.y.zhao@...el.com>
Subject: Re: [PATCH 05/19] mm/gup: Detect huge pfnmap entries in gup-fast

On 09.08.24 18:08, Peter Xu wrote:
> Since gup-fast doesn't have the vma reference, teach it to detect such huge
> pfnmaps by checking the special bit for pmd/pud too, just like ptes.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>   mm/gup.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index d19884e097fd..a49f67a512ee 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -3038,6 +3038,9 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
>   	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
>   		return 0;
>   
> +	if (pmd_special(orig))
> +		return 0;
> +
>   	if (pmd_devmap(orig)) {
>   		if (unlikely(flags & FOLL_LONGTERM))
>   			return 0;
> @@ -3082,6 +3085,9 @@ static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
>   	if (!pud_access_permitted(orig, flags & FOLL_WRITE))
>   		return 0;
>   
> +	if (pud_special(orig))
> +		return 0;
> +
>   	if (pud_devmap(orig)) {
>   		if (unlikely(flags & FOLL_LONGTERM))
>   			return 0;

In gup_fast_pte_range() we check after checking pte_devmap(). Do we want 
to do it in a similar fashion here, or is there a reason to do it 
differently?

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb