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Peter Anvin" , "Peter Zijlstra (Intel)" , Borislav Petkov , Dave Hansen , Ingo Molnar , "Mathieu Desnoyers" , Paolo Bonzini , Sairaj Kodilkar , "Sean Christopherson" , Thomas Gleixner , "Uros Bizjak" , , , CC: , Subject: [PATCH v3 0/2] Add support for cmpxchg16b emulation Date: Wed, 26 Aug 2026 12:30:02 +0530 Message-ID: <20260826070004.8100-1-sarunkod@amd.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain 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: CO1PEPF000066EA:EE_|SN7PR12MB8058:EE_ X-MS-Office365-Filtering-Correlation-Id: ceea8316-179f-4008-9f32-08df033fc19d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|1800799024|23010399003|7416014|376014|36860700016|13003099007|921020|6133799003|10067099003|56012099006|11063799006|18002099003|3023799007; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:149.199.90.133;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:unknown-90-133.xilinx.com;CAT:NONE;SFS:(13230040)(82310400026)(1800799024)(23010399003)(7416014)(376014)(36860700016)(13003099007)(921020)(6133799003)(10067099003)(56012099006)(11063799006)(18002099003)(3023799007);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: iE86GHPR/Sts15npeyV1AD5p1LcaeVAuyZCnaW8XcQjorDTQB1w//uSRTHCQ7zIDMhgxAw1wpry56C9G0+w/68kteygDPhetn0vdqbYbPer7CVn9mBpmz0Hdj3ks5ZnLczFPeGCAqmIACCTtNWJdR9KkL4GDUCKVGd7LsMbO5czGcsWHNdUMXSHmxS8X4sJmGkWwN6HOXKWHThSXerqm/eMz/pNjSHru4kYSVIqlCxLR5oSnGYAMtFTaTH7f4y1od8v+6GFo8R0/P0HIevawVKLKiDYxP9myveWnf4tygbXESliw4QP3mGgVVtlPULnJ8g7hMN9bp6ls9qeSpj/V6tWSGcEXDM3kLfXalpvfVeDxxO61thNWEmixj2kCSnQVofbXXGkLO3VjH12SMYiJavMq0pP3iHEni4OCD0AU/Wd4dji/uApXTtY3y9t5mnIA X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Aug 2026 07:00:47.5273 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ceea8316-179f-4008-9f32-08df033fc19d X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[149.199.90.133];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000066EA.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8058 This series adds 128-bit compare-exchange support needed for KVM to emulate guest cmpxchg16b instructions. The AMD IOMMU driver updates 256-bit device table entries with two 128-bit cmpxchg operations. For hardware-accelerated vIOMMU, QEMU traps those DTE accesses to install nested page tables [1]. KVM must emulate guest cmpxchg16b on the trapped MMIO regions; without that, DTE access emulation fails. Patch 1: extends the x86 user CMPXCHG helpers with __try_cmpxchg128_user_asm() (cmpxchg16b on x86-64), wired into unsafe_try_cmpxchg_user(). Patch 2: extends KVM CMPXCHG8B emulation to 16-byte operands (REX.W=1) and uses the new helper for atomic 16-byte compare-exchange on guest RAM via emulator_cmpxchg_emulated(). You can find the KUT to test this series at [2]. [1] https://github.com/AMDESE/qemu-iommu/blob/wip/for_iommufd_hw_queue-v8_amd_viommu_20260106/hw/i386/amd_viommu.c#L517 [2] https://lore.kernel.org/kvm/20260706062153.346-1-sarunkod@amd.com/T/#u Changes since v2: https://lore.kernel.org/all/20260706063035.1139-1-sarunkod@amd.com/ Patch 1: Trigger build failure if __try_cmpxchg128_user_asm is called on 32 bit machines [Sean] Sairaj Kodilkar (2): x86/uaccess: Extend CMPXCHG user helpers to 128-bit operands KVM: x86: Add support for cmpxchg16b emulation arch/x86/include/asm/uaccess.h | 56 +++++++++++++++++++++++++++++++++- arch/x86/kvm/emulate.c | 50 ++++++++++++++++++++---------- arch/x86/kvm/kvm_emulate.h | 6 ++++ arch/x86/kvm/x86.c | 7 ++++- 4 files changed, 101 insertions(+), 18 deletions(-) base-commit: 45c13f3f9e3bb15fd89ff2864c6f627a3b4b4229 -- 2.34.1