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Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Nadav Amit , Rik van Riel Subject: [PATCH] x86/mm: Skip global ASID broadcast TLB flush when PCID is disabled Date: Wed, 13 May 2026 13:11:25 -0500 Message-ID: <6d67675458bfe4ac1ed792beec3ad93dd45848c7.1778695885.git.thomas.lendacky@amd.com> X-Mailer: git-send-email 2.51.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF00001CDD:EE_|IA1PR12MB8519:EE_ X-MS-Office365-Filtering-Correlation-Id: 8ff5a1d2-15bf-46bf-eef9-08deb11b158d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|7416014|36860700016|82310400026|11063799003|3023799003|18002099003|56012099003; X-Microsoft-Antispam-Message-Info: ByQNRiAmRdyPCg5sQaYitTwTpNQtJyBE2AilU43/FVjv/JHUnFm44V3PDan6XW7Aso6vLVBgp9wyauJ/1vTt0Aw+T+1KCJQNzMe275V0bd+WgKVftRFXpkgjobTcu97iUG+hGWWGlktXJHbpx1YmHnu/3DbLXnFkcVppPY/uu2z8Prl58alo8V9HSWXjNSVWpDU0JcvFGVjD9FKAEhBvggyPdFFvV8oHEusaUoi7EbaeNDTyq+XyMrKh2fzUw7cpu9Qg5K4tfZULCqTC1v3O15TJoyvqfHGCEp+Ye40vU8eIqq6ux6MNsxeoA/0tSp3Ck0ZuHp/iTy7f3A4KrFl5DMd5/jo12NlBZ1jva/T5VpnanaZF/iLdUYMnILV/oBlKllE+vcC52kjV0cbWEiBdTZZeA6nDOGlP+f49svUZTlLzakEtOjXoNehM/fPl9qZsus1uCX1rJOobYJVaJJffxVwoK8CWNd7LHRyDwl/pZmt92D9Ae49GJLMAwfz5Fu8sbUMvQP+6L/goO2ojVWJFrQISMl19JNwxxzLVEl6Y47UFxeHKGbZMBk2KauWyDzqbEpdMlE16dJG+djzT0elaxVffMvxsSt1Rj4tHXuTjWo4IG/69v5kRuChZvGUMf6QGr6zQyZH2fVxEz9JCtHEey+mI0deh2jrI+4ap+4fgjUNuywVpxNezbImj1ewDFPlRHsbjUGjO4L/eve0+0xLS5yyBCgu2Ck2noleleEk+SSg= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(376014)(1800799024)(7416014)(36860700016)(82310400026)(11063799003)(3023799003)(18002099003)(56012099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 85vUO7Qhhqqe3kjyu88O3xOcIkKwixRAe8TsJ48RWrj4eSRtzOIxv21iKnEUq6NncTnNCSP3hNjnfjSW+dwWpQL9ri+H/ygh86tlEWvS97z8tt2dm2dPhCfhgq8grnTbN6Vq+2XbeTjRI5NzDwNZnya3/qi6YyYyESj1871GR/uRHmC52GjENdviUUhKrGjLaWjCqkaibqGAZIk1XO9l4GfX8k4AyTQx7CkxIV9gSYKn2pvr7ea29I6kt7cZzBvHAwu4SNP9bHeO3lIcAsRxgcVC44X+B1QsxKbd0/hNdnN/jWZ2kedNV7CDtVtO8K3d60OkCiKOuWDLg3EBHRWq1H2lOvN3lzMnrv9rIQIXbDMN03aa9olGesqic7tSqaofDzsEZsdDfpDtJmoSpwdCbYu4pGv7GVAXvJN+/UY0Av8VsymnyzSG/qOzgPzLSfA8 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 May 2026 18:11:41.5689 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8ff5a1d2-15bf-46bf-eef9-08deb11b158d X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF00001CDD.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB8519 Content-Type: text/plain; charset="utf-8" Booting with "nopcid" clears X86_FEATURE_PCID in x86_nopcid_setup(), but X86_FEATURE_INVLPGB is left intact. On AMD CPUs that support INVLPGB, broadcast TLB flushing remains active even though CR4.PCIDE is off. There are two checks that decide whether the global ASID code runs, mm_global_asid() and consider_global_asid(), that key off of the X86_FEATURE_INVLPGB feature. Once an mm becomes active on more than three CPUs, consider_global_asid() assigns it a global ASID, after which flush_tlb_mm_range() takes the broadcast_tlb_flush() path. The broadcast_tlb_flush() function calls invlpgb_flush_single_pcid_nosync() or invlpgb_flush_user_nr_nosync() with kern_pcid(asid), which expands to (asid + 1). Both helpers set INVLPGB_FLAG_PCID and place the non-zero PCID into EDX[31:16] of the INVLPGB instruction. Issuing INVLPGB with INVLPGB_FLAG_PCID (RAX[1]) and a non-zero PCID (RDX[27:16]) while CR4.PCIDE is not set results in a #GP: Oops: general protection fault, kernel NULL pointer dereference 0x1: 0000 = [#1] SMP NOPTI CPU: 158 UID: 0 PID: 3119 Comm: snap Not tainted 7.1.0-rc3 #1 PREEMPT(full) Hardware name: ... RIP: 0010:broadcast_tlb_flush+0x9d/0x210 Code: ... 89 da 48 83 c8 07 <0f> 01 fe eb 08 cc cc cc ... RSP: 0000:ffa0000031217cb0 EFLAGS: 00010202 RAX: 00007f8ee8540007 RBX: 0000000008070000 RCX: 0000000000000000 RDX: 0000000000070000 RSI: 0000000000000001 RDI: 00007f8ee8540000 RBP: ff110001189a0700 R08: 00007f8ee8541000 R09: 000000000000000c R10: 000000000000000c R11: 0000000000070000 R12: ff1100c0433aec80 R13: 0000000000000000 R14: 0000000000000008 R15: 0000000000000007 FS: 00007f8ed3fff6c0(0000) GS:ff1100c0b7b8a000(0000) knlGS:00000000000000= 00 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8ee8540058 CR3: 00080001433af000 CR4: 0000000000751ef0 PKRU: 55555554 Call Trace: flush_tlb_mm_range+0xd8/0x220 ptep_clear_flush+0x56/0x60 wp_page_copy+0x293/0x6c0 ? _raw_spin_unlock+0x15/0x30 __handle_mm_fault+0x512/0x6d0 handle_mm_fault+0x145/0x2a0 do_user_addr_fault+0x187/0x6f0 exc_page_fault+0x6a/0x180 asm_exc_page_fault+0x22/0x30 RIP: 0033:0x55c553ebc639 Code: ... RSP: 002b:00007f8ed3ffeaa8 EFLAGS: 00010246 RAX: 00007f8ee8540058 RBX: 000055c554ff77b8 RCX: 00007f8ee853c1c8 RDX: 0000000000000000 RSI: 000000c000062b20 RDI: 00007f8ee8540040 RBP: 00007f8ed3ffeb00 R08: 0000000000006040 R09: 0000000000000005 R10: 0000000000000004 R11: 00000000000001c0 R12: 0000000000000001 R13: 0000005990100204 R14: 000000c000624fc0 R15: 3fffffffffffffff Modules linked in: ... ---[ end trace 0000000000000000 ]--- Add an X86_FEATURE_PCID check to both mm_global_asid() and consider_global_asid() so that the global ASID code is skipped when PCID is disabled. No global ASID is ever allocated under "nopcid", mm_global_asid() always returns 0, and broadcast_tlb_flush() is not reachable. Per-mm flushes fall back to the IPI-based path. The remaining INVLPGB users all pass a PCID value of zero without setting the INVLPGB_FLAG_PCID flag and continue to use the broadcast TLB support. Fixes: 4afeb0ed1753 ("x86/mm: Enable broadcast TLB invalidation for multi-t= hreaded processes") Assisted-by: Claude:claude-opus-4.7 Signed-off-by: Tom Lendacky --- arch/x86/include/asm/tlbflush.h | 3 ++- arch/x86/mm/tlb.c | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflus= h.h index 0545fe75c3fa..c4a9ec78fe69 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -272,7 +272,8 @@ static inline u16 mm_global_asid(struct mm_struct *mm) { u16 asid; =20 - if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB) || + !cpu_feature_enabled(X86_FEATURE_PCID)) return 0; =20 asid =3D smp_load_acquire(&mm->context.global_asid); diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index af43d177087e..e2ace9f056c9 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -445,7 +445,8 @@ static bool mm_needs_global_asid(struct mm_struct *mm, = u16 asid) */ static void consider_global_asid(struct mm_struct *mm) { - if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB) || + !cpu_feature_enabled(X86_FEATURE_PCID)) return; =20 /* Check every once in a while. */ base-commit: 1d5dcaa3bd65f2e8c9baa14a393d3a2dc5db7524 --=20 2.51.1