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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 May 2025 01:40:07.8093 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8ef3f43d-e260-4a6e-1c9e-08dd9a63ea39 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CY4PEPF0000EE37.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB7816 Content-Type: text/plain; charset="utf-8" From: Ankit Agrawal Introduce a new KVM capability to expose to the userspace whether cacheable mapping of PFNMAP is supported. The ability to safely do the cacheable mapping of PFNMAP is contingent on S2FWB and ARM64_HAS_CACHE_DIC. S2FWB allows KVM to avoid flushing the D cache, ARM64_HAS_CACHE_DIC allows KVM to avoid flushing the icache and turns icache_inval_pou() into a NOP. The cap would be false if those requirements are missing and is checked by making use of kvm_arch_supports_cacheable_pfnmap. This capability would allow userspace to discover the support. This would be used in conjunction with the KVM_MEM_ENABLE_CACHEABLE_PFNMAP memslot flag. Userspace is required to query this capability before it can set the memslot flag. This cap could also be used by userspace to prevent live-migration across FWB and non-FWB hosts. CC: Catalin Marinas CC: Jason Gunthorpe CC: Oliver Upton CC: David Hildenbrand Suggested-by: Marc Zyngier Signed-off-by: Ankit Agrawal --- Documentation/virt/kvm/api.rst | 17 ++++++++++++++++- arch/arm64/kvm/arm.c | 7 +++++++ include/uapi/linux/kvm.h | 1 + virt/kvm/kvm_main.c | 3 +++ 4 files changed, 27 insertions(+), 1 deletion(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 47c7c3f92314..ad4c5e131977 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8478,7 +8478,7 @@ ENOSYS for the others. When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request. =20 -7.37 KVM_CAP_ARM_WRITABLE_IMP_ID_REGS +7.42 KVM_CAP_ARM_WRITABLE_IMP_ID_REGS ------------------------------------- =20 :Architectures: arm64 @@ -8496,6 +8496,21 @@ aforementioned registers before the first KVM_RUN. T= hese registers are VM scoped, meaning that the same set of values are presented on all vCPUs in a given VM. =20 +7.43 KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED +------------------------------------------- + +:Architectures: arm64 +:Target: VM +:Parameters: None + +This capability indicate to the userspace whether a PFNMAP memory region +can be safely mapped as cacheable. This relies on the presence of +force write back (FWB) feature support on the hardware. + +The usermode could query this capability and subsequently set the +KVM_MEM_ENABLE_CACHEABLE_PFNMAP memslot flag forming a handshake to +activate the code. + 8. Other capabilities. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 68fec8c95fee..ea34b08237c4 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -402,6 +402,13 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long= ext) case KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES: r =3D BIT(0); break; + case KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED: + if (!kvm) + r =3D -EINVAL; + else + r =3D kvm_arch_supports_cacheable_pfnmap(); + break; + default: r =3D 0; } diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 9defefe7bdf0..fb868586d73d 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -931,6 +931,7 @@ struct kvm_enable_cap { #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237 #define KVM_CAP_X86_GUEST_MODE 238 #define KVM_CAP_ARM_WRITABLE_IMP_ID_REGS 239 +#define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 240 =20 struct kvm_irq_routing_irqchip { __u32 irqchip; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index cddda7f21413..25af7292810c 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1537,6 +1537,9 @@ static int check_memory_region_flags(struct kvm *kvm, { u32 valid_flags =3D KVM_MEM_LOG_DIRTY_PAGES; =20 + if (kvm_arch_supports_cacheable_pfnmap()) + valid_flags |=3D KVM_MEM_ENABLE_CACHEABLE_PFNMAP; + if (kvm_arch_has_private_mem(kvm)) valid_flags |=3D KVM_MEM_GUEST_MEMFD; =20 --=20 2.34.1