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 D90A623B62C for ; Thu, 18 Sep 2025 10:32:11 +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=1758191531; cv=none; b=t7y4DlihLEAQ+hhomWUIRR+he+Gje9HZ7ALXagg+Ka7MxM+OjtHTHHSZ7WIiQ3pZzHSpruBrUNzdmyNLn75r7YLrFyEYEZNBGFAa4Aj29xtvQ4tOcUz5SWrU++r/R2ZRJ7eoNDifT3KTM+9jIuV56VJI6TTBx/ZxGkho+e5n3oQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758191531; c=relaxed/simple; bh=yy2/qGmH2QA2swtXgVVOAHnOxEMhRZ0NhObdYrFdpP8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=WPXD1h5rQt3zyynLG6Q0mx1w1Lv/ebbP2eQbwAJMPkJGFvuOGO+7f0wDeeco2pKeg/7rbvyhBVvbPvbvlYgkmZ3jUOu8p/HPdUlBCYMBGlOIfvAX0CWMOYl2m56gwU5lpnU2HHz3r+mY+1cIsaGkgj2qvrVfU5xssuGDQEbZj1M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=smkYQj59; 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="smkYQj59" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 772E8C4CEFC; Thu, 18 Sep 2025 10:32:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758191531; bh=yy2/qGmH2QA2swtXgVVOAHnOxEMhRZ0NhObdYrFdpP8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=smkYQj59cJEB2MBpLMWEo/hAvXX7jkJTDCXOe2YP6B8kjmfCFAlaw29s3ux/BKgAB BN87ihWMAGN0M8GH5XkkXR5gSQpGbFfOkSdZVWemcu7XAPnuioH89tfzj4ndhqDfRM mrfhGj0JEG72SS2jkPZ4pVFACZ4hfclVKHHxc6f/4ESFCWacU7MYgbI6XOZ/g6HCZ9 Vmq73d/+GCK2p37SXDMw+YFGDctVpPmeikPcp/k3Um83y5bPqrAZTTxnAGCeF2lpS7 zLE1C7TdB7kXGrUvzq9wunjrmFRxhcoyiGYcu2Ij8YlqqHofGS5VPp0T5kp9hz09v+ KWqav/GLcplpA== From: Pratyush Yadav To: Mike Rapoport Cc: Andrew Morton , Alexander Graf , Baoquan He , Changyuan Lyu , Chris Li , Jason Gunthorpe , Pasha Tatashin , Pratyush Yadav , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/4] kho: replace kho_preserve_phys() with kho_preserve_pages() In-Reply-To: <20250917174033.3810435-3-rppt@kernel.org> References: <20250917174033.3810435-1-rppt@kernel.org> <20250917174033.3810435-3-rppt@kernel.org> Date: Thu, 18 Sep 2025 12:32:08 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Hi Mike, On Wed, Sep 17 2025, Mike Rapoport wrote: > From: "Mike Rapoport (Microsoft)" > > to make it clear that KHO operates on pages rather than on a random > physical address. > > The kho_preserve_pages() will be also used in upcoming support for > vmalloc preservation. > > Signed-off-by: Mike Rapoport (Microsoft) > --- > include/linux/kexec_handover.h | 5 +++-- > kernel/kexec_handover.c | 25 +++++++++++-------------- > mm/memblock.c | 4 +++- > 3 files changed, 17 insertions(+), 17 deletions(-) > > diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h > index 348844cffb13..cc5c49b0612b 100644 > --- a/include/linux/kexec_handover.h > +++ b/include/linux/kexec_handover.h > @@ -18,6 +18,7 @@ enum kho_event { > > struct folio; > struct notifier_block; > +struct page; > > #define DECLARE_KHOSER_PTR(name, type) \ > union { \ > @@ -42,7 +43,7 @@ struct kho_serialization; > bool kho_is_enabled(void); > > int kho_preserve_folio(struct folio *folio); > -int kho_preserve_phys(phys_addr_t phys, size_t size); > +int kho_preserve_pages(struct page *page, unsigned int nr_pages); > struct folio *kho_restore_folio(phys_addr_t phys); > int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt); > int kho_retrieve_subtree(const char *name, phys_addr_t *phys); > @@ -65,7 +66,7 @@ static inline int kho_preserve_folio(struct folio *folio) > return -EOPNOTSUPP; > } > > -static inline int kho_preserve_phys(phys_addr_t phys, size_t size) > +static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages) > { > return -EOPNOTSUPP; > } > diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c > index f421acc58c1f..3ad59c5f9eaa 100644 > --- a/kernel/kexec_handover.c > +++ b/kernel/kexec_handover.c > @@ -698,26 +698,23 @@ int kho_preserve_folio(struct folio *folio) > EXPORT_SYMBOL_GPL(kho_preserve_folio); > > /** > - * kho_preserve_phys - preserve a physically contiguous range across kexec. > - * @phys: physical address of the range. > - * @size: size of the range. > + * kho_preserve_pages - preserve contiguous pages across kexec > + * @page: first page in the list. > + * @nr_pages: number of pages. > * > - * Instructs KHO to preserve the memory range from @phys to @phys + @size > - * across kexec. > + * Preserve a contiguous list of order 0 pages. Must be restored using > + * kho_restore_page() on each order 0 page. This is not true. The pages are preserved with the maximum order possible. while (pfn < end_pfn) { const unsigned int order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); err = __kho_preserve_order(track, pfn, order); [...] So four 0-order pages will be preserved as one 2-order page. Restoring them as four 0-order pages is wrong. And my proposed patch for checking the magic [0] will uncover this exact bug. I think you should either change the logic to always preserve at order 0, or maybe add a kho_restore_pages() that replicates the same order calculation. [0] https://lore.kernel.org/lkml/20250917125725.665-2-pratyush@kernel.org/ > * > * Return: 0 on success, error code on failure > */ > -int kho_preserve_phys(phys_addr_t phys, size_t size) > +int kho_preserve_pages(struct page *page, unsigned int nr_pages) > { > - unsigned long pfn = PHYS_PFN(phys); > + struct kho_mem_track *track = &kho_out.ser.track; > + const unsigned long start_pfn = page_to_pfn(page); > + const unsigned long end_pfn = start_pfn + nr_pages; > + unsigned long pfn = start_pfn; > unsigned long failed_pfn = 0; > - const unsigned long start_pfn = pfn; > - const unsigned long end_pfn = PHYS_PFN(phys + size); > int err = 0; > - struct kho_mem_track *track = &kho_out.ser.track; > - > - if (!PAGE_ALIGNED(phys) || !PAGE_ALIGNED(size)) > - return -EINVAL; > > while (pfn < end_pfn) { > const unsigned int order = > @@ -737,7 +734,7 @@ int kho_preserve_phys(phys_addr_t phys, size_t size) > > return err; > } > -EXPORT_SYMBOL_GPL(kho_preserve_phys); > +EXPORT_SYMBOL_GPL(kho_preserve_pages); > > /* Handling for debug/kho/out */ > > diff --git a/mm/memblock.c b/mm/memblock.c > index 117d963e677c..6ec3eaa4e8d1 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -2516,8 +2516,10 @@ static int reserve_mem_kho_finalize(struct kho_serialization *ser) > > for (i = 0; i < reserved_mem_count; i++) { > struct reserve_mem_table *map = &reserved_mem_table[i]; > + struct page *page = phys_to_page(map->start); > + unsigned int nr_pages = map->size >> PAGE_SHIFT; > > - err |= kho_preserve_phys(map->start, map->size); > + err |= kho_preserve_pages(page, nr_pages); Unrelated to this patch, but since there is no kho_restore_{phys,pages}(), won't the reserve_mem memory end up with uninitialized struct pages, since preserved pages are memblock_reserved_mark_noinit()? That would also be a case for kho_restore_pages() I suppose? -- Regards, Pratyush Yadav