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Message-ID: <9b57f325-2dc7-48a4-b2f0-d7daa2192925@lucifer.local>
Date: Mon, 11 Aug 2025 12:46:32 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Dennis Zhou <dennis@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
Andrey Ryabinin <ryabinin.a.a@...il.com>, x86@...nel.org,
Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Tejun Heo <tj@...nel.org>, Uladzislau Rezki <urezki@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Christoph Lameter <cl@...two.org>,
David Hildenbrand <david@...hat.com>,
Andrey Konovalov <andreyknvl@...il.com>,
Vincenzo Frascino <vincenzo.frascino@....com>,
"H. Peter Anvin" <hpa@...or.com>, kasan-dev@...glegroups.com,
Mike Rapoport <rppt@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Suren Baghdasaryan <surenb@...gle.com>, Thomas Huth <thuth@...hat.com>,
John Hubbard <jhubbard@...dia.com>, Michal Hocko <mhocko@...e.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, linux-mm@...ck.org,
"Kirill A. Shutemov" <kas@...nel.org>,
Oscar Salvador <osalvador@...e.de>, Jane Chu <jane.chu@...cle.com>,
Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
Joerg Roedel <joro@...tes.org>, Alistair Popple <apopple@...dia.com>,
Joao Martins <joao.m.martins@...cle.com>, linux-arch@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH V4 mm-hotfixes 3/3] x86/mm/64: define
ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings()
On Mon, Aug 11, 2025 at 02:34:20PM +0900, Harry Yoo wrote:
> Define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings() to ensure
> page tables are properly synchronized when calling p*d_populate_kernel().
> It is inteneded to synchronize page tables via pgd_pouplate_kernel() when
> 5-level paging is in use and via p4d_pouplate_kernel() when 4-level paging
> is used.
>
I think it's worth mentioning here that pgd_populate() is a no-op in 4-level
systems, so the sychronisation must occur at the P4D level, just to make this
clear.
> This fixes intermittent boot failures on systems using 4-level paging
> and a large amount of persistent memory:
>
> BUG: unable to handle page fault for address: ffffe70000000034
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 0 P4D 0
> Oops: 0002 [#1] SMP NOPTI
> RIP: 0010:__init_single_page+0x9/0x6d
> Call Trace:
> <TASK>
> __init_zone_device_page+0x17/0x5d
> memmap_init_zone_device+0x154/0x1bb
> pagemap_range+0x2e0/0x40f
> memremap_pages+0x10b/0x2f0
> devm_memremap_pages+0x1e/0x60
> dev_dax_probe+0xce/0x2ec [device_dax]
> dax_bus_probe+0x6d/0xc9
> [... snip ...]
> </TASK>
>
> It also fixes a crash in vmemmap_set_pmd() caused by accessing vmemmap
> before sync_global_pgds() [1]:
>
> BUG: unable to handle page fault for address: ffffeb3ff1200000
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 0 P4D 0
> Oops: Oops: 0002 [#1] PREEMPT SMP NOPTI
> Tainted: [W]=WARN
> RIP: 0010:vmemmap_set_pmd+0xff/0x230
> <TASK>
> vmemmap_populate_hugepages+0x176/0x180
> vmemmap_populate+0x34/0x80
> __populate_section_memmap+0x41/0x90
> sparse_add_section+0x121/0x3e0
> __add_pages+0xba/0x150
> add_pages+0x1d/0x70
> memremap_pages+0x3dc/0x810
> devm_memremap_pages+0x1c/0x60
> xe_devm_add+0x8b/0x100 [xe]
> xe_tile_init_noalloc+0x6a/0x70 [xe]
> xe_device_probe+0x48c/0x740 [xe]
> [... snip ...]
>
> Cc: <stable@...r.kernel.org>
> Fixes: 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges")
> Closes: https://lore.kernel.org/linux-mm/20250311114420.240341-1-gwan-gyeong.mun@intel.com [1]
> Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Harry Yoo <harry.yoo@...cle.com>
Other than nitty comments, this looks good to me, so:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
> arch/x86/include/asm/pgtable_64_types.h | 3 +++
> arch/x86/mm/init_64.c | 5 +++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 4604f924d8b8..7eb61ef6a185 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -36,6 +36,9 @@ static inline bool pgtable_l5_enabled(void)
> #define pgtable_l5_enabled() cpu_feature_enabled(X86_FEATURE_LA57)
> #endif /* USE_EARLY_PGTABLE_L5 */
>
> +#define ARCH_PAGE_TABLE_SYNC_MASK \
> + (pgtable_l5_enabled() ? PGTBL_PGD_MODIFIED : PGTBL_P4D_MODIFIED)
> +
> extern unsigned int pgdir_shift;
> extern unsigned int ptrs_per_p4d;
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 76e33bd7c556..a78b498c0dc3 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -223,6 +223,11 @@ static void sync_global_pgds(unsigned long start, unsigned long end)
> sync_global_pgds_l4(start, end);
> }
>
Worth a comment to say 'if 4-level, then we synchronise at P4D level by
convention, however the same sync_global_pgds() applies'?
> +void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
> +{
> + sync_global_pgds(start, end);
> +}
> +
> /*
> * NOTE: This function is marked __ref because it calls __init function
> * (alloc_bootmem_pages). It's safe to do it ONLY when after_bootmem == 0.
> --
> 2.43.0
>
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