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Fri, 24 Aug 2018 10:26:52 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) Subject: Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE From: Nadav Amit In-Reply-To: <20180824084717.GK24124@hirez.programming.kicks-ass.net> Date: Fri, 24 Aug 2018 10:26:50 -0700 Cc: Linus Torvalds , Benjamin Herrenschmidt , Nick Piggin , Andrew Lutomirski , the arch/x86 maintainers , Borislav Petkov , Rik van Riel , Jann Horn , Adin Scannell , Dave Hansen , Linux Kernel Mailing List , linux-mm , David Miller , Martin Schwidefsky , Michael Ellerman Content-Transfer-Encoding: quoted-printable Message-Id: References: <20180822153012.173508681@infradead.org> <20180822154046.823850812@infradead.org> <20180822155527.GF24124@hirez.programming.kicks-ass.net> <20180823134525.5f12b0d3@roar.ozlabs.ibm.com> <776104d4c8e4fc680004d69e3a4c2594b638b6d1.camel@au1.ibm.com> <20180823133958.GA1496@brain-police> <20180824084717.GK24124@hirez.programming.kicks-ass.net> To: Peter Zijlstra , Will Deacon X-Mailer: Apple Mail (2.3445.9.1) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org at 1:47 AM, Peter Zijlstra wrote: > On Thu, Aug 23, 2018 at 02:39:59PM +0100, Will Deacon wrote: >> The only problem with this approach is that we've lost track of the = granule >> size by the point we get to the tlb_flush(), so we can't adjust the = stride of >> the TLB invalidations for huge mappings, which actually works nicely = in the >> synchronous case (e.g. we perform a single invalidation for a 2MB = mapping, >> rather than iterating over it at a 4k granule). >>=20 >> One thing we could do is switch to synchronous mode if we detect a = change in >> granule (i.e. treat it like a batch failure). >=20 > We could use tlb_start_vma() to track that, I think. Shouldn't be too > hard. Somewhat unrelated, but I use this opportunity that TLB got your = attention for something that bothers me for some time. clear_fixmap(), which is = used in various places (e.g., text_poke()), ends up in doing only a local TLB flush (in __set_pte_vaddr()). Is that sufficient?