Re: [PATCH v17 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW
From: Yu, Yu-cheng <hidden>
Date: 2021-01-25 22:20:37
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On 1/25/2021 1:55 PM, Borislav Petkov wrote:
On Mon, Jan 25, 2021 at 01:27:51PM -0800, Yu, Yu-cheng wrote:quoted
quoted
Maybe I'm missing something but those two can happen outside of the loop, no? Or is *ptep somehow changing concurrently while the loop is doing the CMPXCHG and you need to recreate it each time? IOW, you can generate upfront and do the empty loop...*ptep can change concurrently.Care to elaborate?
For example, when a thread reads a W=1, D=0 PTE and before changing it to W=0,D=0, another thread could have written to the page and the PTE is W=1, D=1 now. When try_cmpxchg() detects the difference, old_pte is read again.