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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: <20260728150126.GC921102@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> <20260728145528.GI651302@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260728145528.GI651302@noisy.programming.kicks-ass.net> X-Stat-Signature: q7edxor4stk9me5kfr7wxe99fczufrdj X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B49001C0006 X-Rspam-User: X-HE-Tag: 1785250895-924253 X-HE-Meta: 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 KANbqYrm 3dkvqUG90uy8xqMsb47Xy2+GtxjW46tEKCp2JnEv5vaIMzc1JWu5E9cAqQZZD6rOsNGTttUgbnh9jOiOlTtytHEfPtrmxYD/3Odg2Sq/zQMaJ2vpHUgs+Yl4fGQox/C59y3Xr3etiR4zvpDRwibn7t97xmdO5DbhNojFd3BZoMT27Ihai9JWt4czUOzTTlFixE0FM4fSPjEePLqnD4EJjB+gG6ejwS/T8Kh6510bf8REG+HX3cw2IzUDt34aac7Ruc99b/S8lAwOb27CNe7m7PcoX/RlYoqDceVZvzHcseou3eTWV0Hd/7g0TKl9J7YFseNBk/5E137sNwNw= 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 04:55:28PM +0200, Peter Zijlstra wrote: > 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. > Also, the 'atomic context' usage hereabout seems confused. In particular the issue is with IRQ-disabled context, they are not the same thing. This confusion is seen in the existing comments in __set_pages_{p,np}() and in this patch series. It needs fixing.