From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A45C42E11D5 for ; Fri, 13 Jun 2025 16:03:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749830608; cv=none; b=YLvvCgjyCE3AXBgoq59oRSTJUesh1b44kctv3VjicIsV+UE/D5i9zlzjKjAgNfR2I5WEdPD95FkQKf8prNUCkc3qXzWFPoPSuT3bakSpe7kBuVkeIBoStVmZ60g3YoX1oasm1jBeLQdzjFxu4nnpcr+YvVZ3YbXYNoqrINuPRyg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749830608; c=relaxed/simple; bh=hG1xBkodWlqX8knsQvDzVtwCU36MdgTYDKkhHWNjPSw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=j4/FfYWd8321bNSdlSqCKN724xLdmCfBtvqtwmdABdXIp3FlzTcN91d15XxnyhYNC51pItzP41gfJcIXj9wY5tUjw0yvDWcQD9DegfSNBUc/Njjbs1Wub7wzPnM7xiEbx5N7LwbivkCy713QPGHykR77dFuDzsqFMAvVhQJu1AM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mTbIjhbv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mTbIjhbv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 655E6C4CEE3; Fri, 13 Jun 2025 16:03:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749830608; bh=hG1xBkodWlqX8knsQvDzVtwCU36MdgTYDKkhHWNjPSw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250613125916.39272-1-pratyush@kernel.org> 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.