Add a capability to let userspace discover whether guest_memfd supports removing its folios from the direct map. Support depends on guest_memfd itself being supported, but also on whether KVM can manipulate the direct map at page granularity at all (possible most of the time, just arm64 is a notable outlier where its impossible if the direct map has been setup using hugepages, as arm64 cannot break these apart due to break-before-make semantics).
Signed-off-by: Patrick Roy roypat@amazon.co.uk --- include/uapi/linux/kvm.h | 1 + virt/kvm/kvm_main.c | 5 +++++ 2 files changed, 6 insertions(+)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 4654c01a0a01..fb02a93546d8 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -930,6 +930,7 @@ struct kvm_enable_cap { #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237 #define KVM_CAP_X86_GUEST_MODE 238 #define KVM_CAP_GMEM_SHARED_MEM 239 +#define KVM_CAP_GMEM_NO_DIRECT_MAP 240
struct kvm_irq_routing_irqchip { __u32 irqchip; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 3e40acb9f5c0..32ca1c921ab0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -65,6 +65,7 @@ #include <trace/events/kvm.h>
#include <linux/kvm_dirty_ring.h> +#include <linux/set_memory.h>
/* Worst case buffer size needed for holding an integer. */ @@ -4823,6 +4824,10 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) return kvm_supported_mem_attributes(kvm); #endif #ifdef CONFIG_KVM_PRIVATE_MEM + case KVM_CAP_GMEM_NO_DIRECT_MAP: + if (!can_set_direct_map()) + return false; + fallthrough; case KVM_CAP_GUEST_MEMFD: return !kvm || kvm_arch_has_private_mem(kvm); #endif