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Donenfeld" To: Linus Torvalds Cc: David Hildenbrand , linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de, linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , David Hildenbrand , linux-mm@kvack.org Subject: Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings Message-ID: References: <20240709130513.98102-2-Jason@zx2c4.com> <378f23cb-362e-413a-b221-09a5352e79f2@redhat.com> <9b400450-46bc-41c7-9e89-825993851101@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1F7B1C0005 X-Stat-Signature: fniyqsfnn73yjg6u81iix8joy1t8rrnh X-Rspam-User: X-HE-Tag: 1720729046-962696 X-HE-Meta: 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 5wkRLFJV 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 11, 2024 at 10:07:30PM +0200, Jason A. Donenfeld wrote: > Hi Linus, > > On Thu, Jul 11, 2024 at 10:57:17AM -0700, Linus Torvalds wrote: > > May I suggest a slightly different approach: do what we did for "pte_mkwrite()". > > > > It needed the vma too, for not too dissimilar reasons: special dirty > > bit handling for the shadow stack. See > > Thanks for the suggestion. That seems pretty clean. > > It still needs to avoid setting swapbacked in the first place, but > ensuring that it's never dirty means it won't get turned back on. > > The first patch renames pte_dirty() to pte_dirty_novma(). The second > patch adds an inline function, pte_dirty(pte, vma) that just forwards > the pte to pte_dirty_novma(), and then converts callers that have a vma > available to pass to call pte_dirty(). And then the VM_DROPPABLE patch > simply adds the `&& !(vma->vm_flags & VM_DROPPABLE)` condition to > pte_dirty(). > > I put these in https://git.zx2c4.com/linux-rng/log/ per usual, and I'll > post a new version to the list not before long (unless objections). Oh, I didn't catch upthread in time (my mail flow is based on `lei up`, which I guess I should run at greater frequency). It seems like we apparently might go in a different direction. I'll move that to https://git.zx2c4.com/linux-rng/log/?h=jd/pte_dirty in case it's useful later, though. Jason