linux-kernel - Re: [PATCH v2 12/39] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE

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Message-Id: <BF99C63D-670D-40B4-98DC-22E9F416244E@gmail.com>
Date:   Mon, 3 Oct 2022 17:40:33 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH v2 12/39] x86/mm: Update ptep_set_wrprotect() and
 pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW

On Oct 3, 2022, at 4:38 PM, Edgecombe, Rick P <rick.p.edgecombe@...el.com> wrote:

> I think the HW dirty bit will not be set here. How it works is,
> pte_mkdirty() will not actually set the HW dirty bit, but instead the
> software COW bit. Here is the relevant snippet:
> 
> static inline pte_t pte_mkdirty(pte_t pte)
> {
> 	pteval_t dirty = _PAGE_DIRTY;
> 
> 	/* Avoid creating Dirty=1,Write=0 PTEs */
> 	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pte_write(pte))
> 		dirty = _PAGE_COW;
> 
> 	return pte_set_flags(pte, dirty | _PAGE_SOFT_DIRTY);
> }
> 
> So for a !VM_WRITE vma, you end up with Write=0,Cow=1 PTE passed
> into ptep_set_access_flags(). Does it make sense?

Thanks for your patience with me. I should have read the series in order.