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 DC4A824EF6B for ; Fri, 6 Jun 2025 08:04:46 +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=1749197086; cv=none; b=saSgPV+iAcozIH8s7wvKl6tOAT4BYTkWL487Yl66zF721A0XfD/llR2gkJp6rLTKD4G7pdqjFgoea2f7wsQo/dl1dXMlQLvgHyq6NwRL1yOgIhoAyIepyKTBzzb8F2lL4Bswgt3xgnKgPZzZ4WF+4GtTZNNpc0bUb7PFVayV7cg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749197086; c=relaxed/simple; bh=/eAbsE62fKUCaEC3zAvD15WyaOeeMA6jncyNVQwRldg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=IqICIVloqDydMg0Sw9vDbvIxDfVG9vEoneZ+BdzR/l9LcLVl+LhyFnVxYw17OlmqIdqdtWdgewQDAaN/u2WpzPzzUq6g3/Nysn9WgQujDgDuoP1BHV+J+PqTRV0XHLMKvW3z0GHtEyRu3o4/RfOXWIrLy6Bir8u7fFZXWZNfnx0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qV4jtDv+; 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="qV4jtDv+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E7EB2C4CEEB; Fri, 6 Jun 2025 08:04:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749197086; bh=/eAbsE62fKUCaEC3zAvD15WyaOeeMA6jncyNVQwRldg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qV4jtDv+PQOS1Z54jDelm+RkHP6SZV4PHiNcZ7pa3FEoaNtqdWNmfGY+gApAqOlfr wGx1+FACRrsQAzZ7HF9ROT3Oc5yRqgeEgYkSwrTVslT3taQMq7DRWpcBnKbjam0jkh FzS4NAgwzQCOJUMLwIGww+BNzcXdv9D8Bu/UY5PY8mAeCL0jBg78dfowP/RdmO1GY/ 8j3RSNfj4DPOJccGvQK70atOh8UnIKDqhJUl+2qw041PRIdtXhzL7igODq4SbPy5HR 5rPxt5E3JOIiJPjdgUc338VwGktz2mCgS5JNdfiK6ss7hQbT9oVG4g04Klb/wQr2zS TmnoqI11hBOfQ== Date: Fri, 6 Jun 2025 11:04:39 +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] kho: initialize tail pages for higher order folios properly Message-ID: References: <20250605171143.76963-1-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: <20250605171143.76963-1-pratyush@kernel.org> On Thu, Jun 05, 2025 at 07:11:41PM +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 > --- > > Side note: get_maintainers.pl for KHO only lists kexec@ as the mailing list. > Since KHO has a bunch of MM bits as well, should we also add linux-mm@ to its > MAINTAINERS entry? > > Adding linux-mm@ to this patch at least, in case MM people have an opinion on > this. > > 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..5214ab27d1f8d 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); So now we don't clear PG_Reserved even on order-0 pages? ;-) > - init_page_count(page); > - adjust_managed_page_count(page, 1); > + unsigned int i, nr_pages = (1 << order); Can you please declare 'i' inside the loop, looks nicer IMHO. > + > + /* Head page gets refcount of 1. */ > + set_page_count(page, 1); ClearPageReserved(page) here? > + > + /* For higher order folios, tail pages get a page count of zero. */ > + for (i = 1; i < nr_pages; i++) > + set_page_count(page + i, 0); and here? > + > + 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.