Messages in this thread | | | Date | Sun, 13 Nov 2022 18:56:30 -0500 | From | Peter Xu <> | Subject | Re: [PATCH v2 1/2] mm/migrate: Fix read-only page got writable when recover pte |
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On Fri, Nov 11, 2022 at 10:42:13AM +1100, Alistair Popple wrote: > Hi Peter, for the patch feel free to add: > > Reviewed-by: Alistair Popple <apopple@nvidia.com>
Will do, thanks.
> > I did wonder if this should be backported further for migrate_vma as > well given that a migration failure there might lead a shmem read-only > PTE to become read-write. I couldn't think of an obvious reason why that > would cause an actual problem though. > > I think folio_mkclean() will wrprotect the pte for writeback to swap, > but it holds the page lock which prevents migrate_vma installing > migration entries in the first place. > > I suppose there is a small window there because migrate_vma will unlock > the page before removing the migration entries. So to be safe we could > consider going back to 8763cb45ab96 ("mm/migrate: new memory migration > helper for use with device memory") but I doubt in practice it's a real > problem.
IIRC migrate_vma API only supports anonymous memory, then it's not affected by this issue?
One thing reminded me is I thought mprotect could be affected but I think it's actually not, because mprotect is vma-based, and that should always be fine with current mk_pte(). I'll remove the paragraph on mprotect in the commit message; that could be slightly misleading.
-- Peter Xu
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