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b=mTbIjhbv403WQAi4DQhff37b4AZJdRbbOsyAhYxEmvNGe5nqHK3GKZCI8clTkieZO SjPQH6KWEDyjFnx8L+ivKgXfl+1fEYOi5ad7nPWoKCC2Mvm2CDJo7qVwp/qXZOhYmC tYtbxnA2htUFOSeATzYOk4JoHzVKEJSJChnbgxl7/yAqSuHwKtLf82OEFbB8uJOg2J /aQohI2FCyxuNzXEhzmHdk1u3yj7KyFSsUY3b89ZjNWgEbGBSE/FpCL+df2eGoNAx7 ZHvFOOA8wX/leY2BeRBUAyIIdIZPICGxhPn9j+4SJgez0K4ZF5uszIQPM9EOrvmGBZ afj84W/1P4/nQ== Date: Fri, 13 Jun 2025 19:03:21 +0300 From: Mike Rapoport To: Pratyush Yadav Cc: Alexander Graf , Changyuan Lyu , Pasha Tatashin , Andrew Morton , Baoquan He , Pratyush Yadav , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] kho: initialize tail pages for higher order folios properly Message-ID: References: <20250613125916.39272-1-pratyush@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250613125916.39272-1-pratyush@kernel.org> X-Rspamd-Queue-Id: 784B818001A X-Rspamd-Server: rspam07 X-Stat-Signature: ztdxmxx4euair9xcbqxezhdtytx6wdc7 X-Rspam-User: X-HE-Tag: 1749830609-734841 X-HE-Meta: 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 hWJxJXLw ZUzB2Zv9hYyQ4y2kRkrmw4TKYxaceLJm4wGT1Fqm8lBb/eexg4PX9lkX/S3FLvVd2YxcVCaGw4jCGCLgXtSmhvqVRShwvErPNzca/oiYnlrfTX10ShADCyEuhZXsp8Cq5fGhRApTEgk7Y/IK7Obho6kT1SSeGz5XLX9HaFnWWkJAYrnPQpgzUZ3y1wJsRZ+SHCvzSiij8xw0jGMYFeklH+r60O8mqKain5QUVhajh2v3YB9QsfZAR6l6YLWHyYH4QBzRPA/8b7CacjaxPCDNX3JFdSg== 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 Fri, Jun 13, 2025 at 02:59:06PM +0200, Pratyush Yadav wrote: > From: Pratyush Yadav > > Currently, when restoring higher order folios, kho_restore_folio() only > calls prep_compound_page() on all the pages. That is not enough to > properly initialize the folios. The managed page count does not > get updated, the reserved flag does not get dropped, and page count does > not get initialized properly. > > Restoring a higher order folio with it results in the following BUG with > CONFIG_DEBUG_VM when attempting to free the folio: > > BUG: Bad page state in process test pfn:104e2b > page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffffffffffffffff pfn:0x104e2b > flags: 0x2fffff80000000(node=0|zone=2|lastcpupid=0x1fffff) > raw: 002fffff80000000 0000000000000000 00000000ffffffff 0000000000000000 > raw: ffffffffffffffff 0000000000000000 00000001ffffffff 0000000000000000 > page dumped because: nonzero _refcount > [...] > Call Trace: > > dump_stack_lvl+0x4b/0x70 > bad_page.cold+0x97/0xb2 > __free_frozen_pages+0x616/0x850 > [...] > > Combine the path for 0-order and higher order folios, initialize the > tail pages with a count of zero, and call adjust_managed_page_count() to > account for all the pages instead of just missing them. > > In addition, since all the KHO-preserved pages get marked with > MEMBLOCK_RSRV_NOINIT by deserialize_bitmap(), the reserved flag is not > actually set (as can also be seen from the flags of the dumped page in > the logs above). So drop the ClearPageReserved() calls. > > Fixes: fc33e4b44b271 ("kexec: enable KHO support for memory preservation") > Signed-off-by: Pratyush Yadav Reviewed-by: Mike Rapoport (Microsoft) > --- > > Changes in v2: > - Declare i in the loop instead of at the top. > > kernel/kexec_handover.c | 29 +++++++++++++++++------------ > 1 file changed, 17 insertions(+), 12 deletions(-) > > diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c > index eb305e7e61296..ca525f794f6be 100644 > --- a/kernel/kexec_handover.c > +++ b/kernel/kexec_handover.c > @@ -157,11 +157,21 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn, > } > > /* almost as free_reserved_page(), just don't free the page */ > -static void kho_restore_page(struct page *page) > +static void kho_restore_page(struct page *page, unsigned int order) > { > - ClearPageReserved(page); > - init_page_count(page); > - adjust_managed_page_count(page, 1); > + unsigned int nr_pages = (1 << order); > + > + /* Head page gets refcount of 1. */ > + set_page_count(page, 1); > + > + /* For higher order folios, tail pages get a page count of zero. */ > + for (unsigned int i = 1; i < nr_pages; i++) > + set_page_count(page + i, 0); > + > + if (order > 0) > + prep_compound_page(page, order); > + > + adjust_managed_page_count(page, nr_pages); > } > > /** > @@ -179,15 +189,10 @@ struct folio *kho_restore_folio(phys_addr_t phys) > return NULL; > > order = page->private; > - if (order) { > - if (order > MAX_PAGE_ORDER) > - return NULL; > - > - prep_compound_page(page, order); > - } else { > - kho_restore_page(page); > - } > + if (order > MAX_PAGE_ORDER) > + return NULL; > > + kho_restore_page(page, order); > return page_folio(page); > } > EXPORT_SYMBOL_GPL(kho_restore_folio); > -- > 2.47.1 > -- Sincerely yours, Mike.