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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tgJXK-0000000H8Os-3MKS; Fri, 07 Feb 2025 08:16:31 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CC214300310; Fri, 7 Feb 2025 09:16:29 +0100 (CET) Date: Fri, 7 Feb 2025 09:16:29 +0100 From: Peter Zijlstra To: Rik van Riel Cc: Oleksandr Natalenko , x86@kernel.org, linux-kernel@vger.kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.com, nadav.amit@gmail.com, thomas.lendacky@amd.com, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, jannh@google.com, mhklinux@outlook.com, andrew.cooper3@citrix.com Subject: Re: [PATCH v9 00/12] AMD broadcast TLB invalidation Message-ID: <20250207081629.GT7145@noisy.programming.kicks-ass.net> References: <20250206044346.3810242-1-riel@surriel.com> <12602226.O9o76ZdvQC@natalenko.name> <8111558b52cec1152746b05a9c1d657d18df0fe2.camel@surriel.com> <20250206142308.GR7145@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4EA70A0019 X-Stat-Signature: 7kg1orbmhc1xcy6fkoa43ch6rhsbgxao X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1738916201-79914 X-HE-Meta: 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 M/qwfg5U +Wn4ayUSW/GV5jIL5ot9/3/5bU/q1f7cBiqb/6kXoarZPQeMT9cwkGSaXEo5wBHmgPRGYIYPXu4idcIn0q15nZ6bkBgo5x7ozKEgDmMkLR4bY+WzsczUm7bfy3VZCMs8ZywVwBlhGQxv/jdG2YkKkmz/TQzcQYCahPnpf6EZ71P0JIiScLnM0xe+cYTI+VTZCv4tXvUKaJFtLIuHBD9jvXwZ8SSU59yMKmk3xFXeHFvRcGsy+U8fM/AIcO3gCSdugvYzCVf2zCqevlWA= 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, Feb 06, 2025 at 09:48:25AM -0500, Rik van Riel wrote: > On Thu, 2025-02-06 at 15:23 +0100, Peter Zijlstra wrote: > > On Thu, Feb 06, 2025 at 09:16:35AM -0500, Rik van Riel wrote: > > > > > This can result in flush_tlb_mm_range being called > > > with a stride_shift for 2MB pages, but a range ending > > > on a 4kB aligned (not 2MB aligned) boundary. > > > > > > Peter, how should we solve this one? > > > > I don't think that's wrong per-se, since all we really need is for > > end > > to be past the end, one byte, one page, or one stride don't matter > > much. > > > > Anyway, I'm in desperate need of a break, so I'm not quite sure what > > the > > best way forward is. > > > Given that the tlb_flush() code is used only for > page table freeing, mmu_gather is used for both page and page-table freeing. > we can just round up the > end address to the nearest stride boundary > there, with a comment explaining why? Well, why are we rounding at all? I don't think I've seen an explanation for that anywhere yet. What made you do this? > Alternatively, we could just change the page > sizes used in pmd_free_tlb, pud_free_tlb, > and p4d_free_tlb, given that the functions > called now have parameters they didn't seem > to have back in 2014, when the linked email > in the comment was written? Well, it really shouldn't matter. Notably, stride is simply the smallest size encountered during the gather; not something that can be determined a priory. Like I said, end is exclusive, so it doesn't really matter how much further it is, and PAGE_SIZE is a natural enough step, seeing it is the smallest granularity. So start and end not being page aligned is a definite fail. And start should be stride aligned. But other than that, I don't see it matters much.