linux-kernel - Re: [PATCH] mmu_notifiers: Notify on pte permission upgrades

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Message-ID: <ZGuFu0VwRfZszABB@arm.com>
Date:   Mon, 22 May 2023 16:09:47 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Alistair Popple <apopple@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, robin.murphy@....com,
        will@...nel.org, nicolinc@...dia.com,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, jgg@...dia.com,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH] mmu_notifiers: Notify on pte permission upgrades

On Mon, May 22, 2023 at 04:37:25PM +1000, Alistair Popple wrote:
> diff --git a/mm/memory.c b/mm/memory.c
> index f526b9152bef..0ac78c6a232c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2098,6 +2098,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  	struct mm_struct *mm = vma->vm_mm;
>  	pte_t *pte, entry;
>  	spinlock_t *ptl;
> +	bool changed = false;
>  
>  	pte = get_locked_pte(mm, addr, &ptl);
>  	if (!pte)
> @@ -2120,8 +2121,10 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>  			}
>  			entry = pte_mkyoung(*pte);
>  			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> -			if (ptep_set_access_flags(vma, addr, pte, entry, 1))
> +			if (ptep_set_access_flags(vma, addr, pte, entry, 1)) {
>  				update_mmu_cache(vma, addr, pte);
> +				changed = true;
> +			}
>  		}
>  		goto out_unlock;
>  	}

I haven't checked all the corner cases but can we not have a
ptep_set_access_flags_notify() that handles this (and the huge
equivalent)? It matches the other API like ptep_clear_flush_notify().

-- 
Catalin