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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwN0C-0000000BKmy-3NsY; Wed, 10 Sep 2025 15:44:56 +0000 Date: Wed, 10 Sep 2025 16:44:56 +0100 From: Matthew Wilcox To: Pratyush Yadav Cc: Alexander Graf , Mike Rapoport , Changyuan Lyu , Andrew Morton , Baoquan He , Pasha Tatashin , Jason Gunthorpe , Chris Li , Jason Miu , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH] kho: make sure folio being restored is actually from KHO Message-ID: References: <20250910153443.95049-1-pratyush@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250910153443.95049-1-pratyush@kernel.org> X-Rspamd-Queue-Id: 0FD5A10000D X-Stat-Signature: 74gkh7kx961ma7erx75asc7c7qb3sysq X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1757519101-967769 X-HE-Meta: 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 Zw6r3Lrz SVPwj7BZMZLIdgsEEgpaUqMj9AmAJX0WdSxJV02yJNnv8qhCh9N4SgmH6CcGTgt1mplCl44LbSo5RgMnLguPdsseKoe2EexbFPOhmsxVt0jal8DtE+pWC2CCAgHlwT9BG6pFWlZoW9reG3LU= 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 Wed, Sep 10, 2025 at 05:34:40PM +0200, Pratyush Yadav wrote: > +#define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */ > + > +/* > + * KHO uses page->private, which is an unsigned long, to store page metadata. > + * Use it to store both the magic and the order. > + */ > +union kho_page_info { > + unsigned long page_private; > + struct { > + unsigned int order; > + unsigned int magic; > + }; KHO is only supported on 64-bit? > @@ -210,16 +226,16 @@ static void kho_restore_page(struct page *page, unsigned int order) > struct folio *kho_restore_folio(phys_addr_t phys) > { > struct page *page = pfn_to_online_page(PHYS_PFN(phys)); > - unsigned long order; > + union kho_page_info info; > > if (!page) > return NULL; > > - order = page->private; > - if (order > MAX_PAGE_ORDER) > + info.page_private = page->private; > + if (info.magic != KHO_PAGE_MAGIC || info.order > MAX_PAGE_ORDER) > return NULL; > > - kho_restore_page(page, order); > + kho_restore_page(page, info.order); > return page_folio(page); This all looks very confused. Before your patch as well as after it. I don't see anything in the current KHO code that requires the phys_addr_t to be order-aligned.