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 E3C0F302756; Sat, 7 Feb 2026 10:37:02 +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=1770460623; cv=none; b=Wkn9Ctv1u5Dem/kQyEmu6WRAx9HkoSAlAqxoJbgYYOUSgexbSvwzspegBnmJLJXlkHYn4Li/4+91sQyeAiE2B25GjSGFXUiCpK0zgUltCDgSkhAiKGPfwzsb3nvVNiFf+xiHeMOtVnMJhRN1voPP6u9ShuVNozWJtKI5dDa4H2E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770460623; c=relaxed/simple; bh=5txootZk9XnxQipltUnu1uJG2kCaI77i7XiNzSKLg6I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=t14+WNwUfeSF2E8XvenwNa9dFI5isP5e86o6IKvE5VegWRY22s0na/r+vCypBPheekR9RRszn3j3a39y36TTAvh4oh2CRYAd2GSModpvpYxtQFKGzkdB3eeq8tkzWRRVI9YKL9GeJliq7hzoRnQm/KgyADnHk6741xt6j4c2wtI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cfYuL09Y; 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="cfYuL09Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7A2BFC116D0; Sat, 7 Feb 2026 10:36:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770460622; bh=5txootZk9XnxQipltUnu1uJG2kCaI77i7XiNzSKLg6I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cfYuL09YPhGMJd7P35kyjr0lAxa/iHu/YfsEkzH8LubrxmisxkzKdBFcs1Y2N2MU2 dvs+BpQiIMu7RNuFgOa2U4lhfkQQMWEApPyUIFI4G5jPDx5SxM7vGgvEgcMaAZR3wb b5TmWeYHqGOnIP6RUJQS0EZeSOfMx7DmDO3xOwzBoST0J5Zd5mVF9jwQn1yVKcNfBE uWSTfKP2vKbdUd2LRGCkPloiDZT2rrMv/eHBuetCIurcEWl+GxWXDT1apLvIJsW7lK ecWz7qUsRKRAGOnHYFNSzWF/NyB7DB8z+ZPDngeTtgHQpWl15K7AQ1eM41lt8lTvb6 U9okHU4kls45Q== Date: Sat, 7 Feb 2026 12:36:43 +0200 From: Mike Rapoport To: Andreas Larsson Cc: Andrew Morton , Borislav Petkov , Brian Cain , Catalin Marinas , "David S. Miller" , Dave Hansen , David Hildenbrand , Dinh Nguyen , Geert Uytterhoeven , Guo Ren , Helge Deller , Huacai Chen , Ingo Molnar , Johannes Berg , John Paul Adrian Glaubitz , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Magnus Lindholm , Matt Turner , Max Filippov , Michael Ellerman , Michal Hocko , Michal Simek , Palmer Dabbelt , Richard Weinberger , Russell King , Stafford Horne , Suren Baghdasaryan , Thomas Gleixner , Vineet Gupta , Vlastimil Babka , Will Deacon , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH mm-unstable] arch, mm: consolidate empty_zero_page Message-ID: References: <20260124095628.668870-1-rppt@kernel.org> <2157220c-0394-40fa-9918-a8514171bd10@gaisler.com> 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: On Tue, Feb 03, 2026 at 11:17:08AM +0100, Andreas Larsson wrote: > On 2026-01-27 19:11, Mike Rapoport wrote: > > On Tue, Jan 27, 2026 at 05:02:39PM +0100, Andreas Larsson wrote: > >> On 2026-01-24 10:56, Mike Rapoport wrote: > >> > >>> Every architecture defines empty_zero_page that way or another, but for the > >>> most of them it is always a page aligned page in BSS and most definitions > >>> of ZERO_PAGE do virt_to_page(empty_zero_page). > >> > >> Running this in an LDOM on an UltraSparc T4 sparc64, the entire LDOM > >> hangs after a while during boot. > >> > >>> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c > >>> index c2d19c9a9244..2bd99944176d 100644 > >>> --- a/arch/sparc/mm/init_64.c > >>> +++ b/arch/sparc/mm/init_64.c > >>> @@ -177,9 +177,6 @@ extern unsigned long sparc_ramdisk_image64; > >>> extern unsigned int sparc_ramdisk_image; > >>> extern unsigned int sparc_ramdisk_size; > >>> > >>> -struct page *mem_map_zero __read_mostly; > >>> -EXPORT_SYMBOL(mem_map_zero); > >>> - > >>> unsigned int sparc64_highest_unlocked_tlb_ent __read_mostly; > >>> > >>> unsigned long sparc64_kern_pri_context __read_mostly; > >>> @@ -2506,18 +2503,6 @@ void __init mem_init(void) > >>> */ > >>> register_page_bootmem_info(); > >>> > >>> - /* > >>> - * Set up the zero page, mark it reserved, so that page count > >>> - * is not manipulated when freeing the page from user ptes. > >>> - */ > >>> - mem_map_zero = alloc_pages(GFP_KERNEL|__GFP_ZERO, 0); > >>> - if (mem_map_zero == NULL) { > >>> - prom_printf("paging_init: Cannot alloc zero page.\n"); > >>> - prom_halt(); > >>> - } > >>> - mark_page_reserved(mem_map_zero); > >>> - > >>> - > >>> if (tlb_type == cheetah || tlb_type == cheetah_plus) > >>> cheetah_ecache_flush_init(); > >>> } > >> > >> This just removes the mark_page_reserved(mem_map_zero) without > >> replacing it with something corresponding to that. Perhaps part > >> of the problem? > > > > I don't think so, empty_zero_page is in BSS now an it's reserved as a part > > of the kernel image. > > > > I suspect that virt_to_page() does not work BSS symbols on sparc64. Can you > > please try with this patch: > > > > diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h > > index 74ede706fb32..0578c5172d4e 100644 > > --- a/arch/sparc/include/asm/pgtable_64.h > > +++ b/arch/sparc/include/asm/pgtable_64.h > > @@ -22,6 +22,7 @@ > > #include > > #include > > #include > > +#include > > > > /* The kernel image occupies 0x4000000 to 0x6000000 (4MB --> 96MB). > > * The page copy blockops can use 0x6000000 to 0x8000000. > > @@ -210,6 +211,11 @@ extern unsigned long _PAGE_CACHE; > > extern unsigned long pg_iobits; > > extern unsigned long _PAGE_ALL_SZ_BITS; > > > > +extern unsigned long kern_base; > > +#define ZERO_PAGE(vaddr) \ > > + (virt_to_page(empty_zero_page + ((unsigned long)__va(kern_base)) - \ > > + ((unsigned long)KERNBASE))) > > + > > /* PFNs are real physical page numbers. However, mem_map only begins to record > > * per-page information starting at pfn_base. This is to handle systems where > > * the first physical page in the machine is at some huge physical address, > > diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c > > index 2bd99944176d..d2d724ba4f83 100644 > > --- a/arch/sparc/mm/init_64.c > > +++ b/arch/sparc/mm/init_64.c > > @@ -170,6 +170,8 @@ static void __init read_obp_memory(const char *property, > > > > /* Kernel physical address base and size in bytes. */ > > unsigned long kern_base __read_mostly; > > +EXPORT_SYMBOL(kern_base); > > + > > unsigned long kern_size __read_mostly; > > > > /* Initial ramdisk setup */ > Hi, > > Unfortunately, that does not help. The LDOM goes down in the same fashion. Apparently something is wrong with my pointer arithmetics :/ Can you try this one instead? diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h index 74ede706fb32..615f460c50af 100644 --- a/arch/sparc/include/asm/pgtable_64.h +++ b/arch/sparc/include/asm/pgtable_64.h @@ -210,6 +210,9 @@ extern unsigned long _PAGE_CACHE; extern unsigned long pg_iobits; extern unsigned long _PAGE_ALL_SZ_BITS; +extern struct page *mem_map_zero; +#define ZERO_PAGE(vaddr) (mem_map_zero) + /* PFNs are real physical page numbers. However, mem_map only begins to record * per-page information starting at pfn_base. This is to handle systems where * the first physical page in the machine is at some huge physical address, diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c index 2bd99944176d..aa1f9f071fb2 100644 --- a/arch/sparc/mm/init_64.c +++ b/arch/sparc/mm/init_64.c @@ -177,6 +177,9 @@ extern unsigned long sparc_ramdisk_image64; extern unsigned int sparc_ramdisk_image; extern unsigned int sparc_ramdisk_size; +struct page *mem_map_zero __read_mostly; +EXPORT_SYMBOL(mem_map_zero); + unsigned int sparc64_highest_unlocked_tlb_ent __read_mostly; unsigned long sparc64_kern_pri_context __read_mostly; @@ -2495,6 +2498,9 @@ static void __init register_page_bootmem_info(void) } void __init mem_init(void) { + phys_addr_t zero_page_pa = kern_base + + ((unsigned long)&empty_zero_page[0] - KERNBASE); + /* * Must be done after boot memory is put on freelist, because here we * might set fields in deferred struct pages that have not yet been @@ -2503,6 +2509,12 @@ void __init mem_init(void) */ register_page_bootmem_info(); + /* + * Set up the zero page, mark it reserved, so that page count + * is not manipulated when freeing the page from user ptes. + */ + mem_map_zero = pfn_to_page(PHYS_PFN(zero_page_pa)); + if (tlb_type == cheetah || tlb_type == cheetah_plus) cheetah_ecache_flush_init(); } -- Sincerely yours, Mike.