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Howlett" , Lorenzo Stoakes , Lu Baolu , "H. Peter Anvin" , Shakeel Butt , Suren Baghdasaryan , Thomas Gleixner , Toshi Kani , Vishal Moola , Vlastimil Babka , Will Deacon , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 1/5] x86/mm/pat: introcude cpa_lock() and cpa_unlock() Message-ID: <20260728145528.GI651302@noisy.programming.kicks-ass.net> References: <20260728-cpa-fixes-v1-0-2ed2352300b3@kernel.org> <20260728-cpa-fixes-v1-1-2ed2352300b3@kernel.org> <20260728142108.GW751831@noisy.programming.kicks-ass.net> <20260728143135.GG651302@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 192641C000F X-Rspam-User: X-Stat-Signature: 364eiyfygooi8tthuwi9pp46niguhszo X-HE-Tag: 1785250536-545362 X-HE-Meta: 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 tg4F7Yix 7lYs25DRhL0pzmbysJyEn6P7tXISQpV15jb4jf7Ge2pl+OqbM+4q9GsICNUqZ4i1s2IorhjZ4Bt/GraDOuexyJSiIGeUHFmLJO6ColjFQOthHt72718oMKPH88HYFDXcGEjWCHae3r7FNPB4N5FNiCQWt7/zkLNoW7/BQMcj9TXojPCUs23uXuiYx7uciqAVn09WLvZaX9NL0+SNjXtF9p4Y+vKKhYQqHAwIgfPAk89rXgiZBikRYJLDAA0v81QdpahkqmFX9TWqXsk5kgvEKLvZHmX+2SD7b1D/HEo7SocCZQ/o99Oaa3fKNL4ElYoKvLn0YuE/Tr5bVPTmgZ8QYncusP1zugmYILh/You3mrDr+bOg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 28, 2026 at 05:46:30PM +0300, Mike Rapoport wrote: > On Tue, Jul 28, 2026 at 04:31:35PM +0200, Peter Zijlstra wrote: > > On Tue, Jul 28, 2026 at 07:30:27AM -0700, Dave Hansen wrote: > > > On 7/28/26 07:21, Peter Zijlstra wrote: > > > > There was already a patch merged that removed the shole debug_pagealloc > > > > exception. Is that not better? > > > > > > As I'm scanning through email this morning, there's another issue that > > > popped up with that patch. It's causing hangs on boot. > > > > > > It's looking like debug pagealloc not taking the lock is actually > > > functional, not an optimization. Although, I hesitate to say > > > "functional" and would prefer to use much less nice words to describe it. > > > > Yeah, lets figure out why that is before we retain this wart ;-) > > As Lorenzo said: > > __kernel_map_pages() can be called from irq context: > > < GFP_ATOMIC context > > kfree() or whatever > -> ... > -> __free_pages_prepare() > -> debug_pagealloc_unmap_pages() > -> __kernel_map_pages() > -> __change_page_attr_set_clr() > -> cpa_lock > The TLBI hack in __kernel_map_pages() makes me wonder how any of this is correct to begin with. That comment isn't helping.