From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
David Hildenbrand <david@redhat.com>,
Fuad Tabba <tabba@google.com>,
Ackerley Tng <ackerleytng@google.com>
Subject: [PATCH v2 05/13] KVM: guest_memfd: Allow mmap() on guest_memfd for x86 VMs with private memory
Date: Fri, 3 Oct 2025 16:25:58 -0700 [thread overview]
Message-ID: <20251003232606.4070510-6-seanjc@google.com> (raw)
In-Reply-To: <20251003232606.4070510-1-seanjc@google.com>
Allow mmap() on guest_memfd instances for x86 VMs with private memory as
the need to track private vs. shared state in the guest_memfd instance is
only pertinent to INIT_SHARED. Doing mmap() on private memory isn't
terrible useful (yet!), but it's now possible, and will be desirable when
guest_memfd gains support for other VMA-based syscalls, e.g. mbind() to
set NUMA policy.
Lift the restriction now, before MMAP support is officially released, so
that KVM doesn't need to add another capability to enumerate support for
mmap() on private memory.
Fixes: 3d3a04fad25a ("KVM: Allow and advertise support for host mmap() on guest_memfd files")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 7 ++++---
include/linux/kvm_host.h | 12 +++++++++++-
virt/kvm/guest_memfd.c | 9 ++-------
virt/kvm/kvm_main.c | 6 +-----
4 files changed, 18 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4b8138bd4857..fe3dc3eb4331 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13942,10 +13942,11 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
#ifdef CONFIG_KVM_GUEST_MEMFD
/*
- * KVM doesn't yet support mmap() on guest_memfd for VMs with private memory
- * (the private vs. shared tracking needs to be moved into guest_memfd).
+ * KVM doesn't yet support initializing guest_memfd memory as shared for VMs
+ * with private memory (the private vs. shared tracking needs to be moved into
+ * guest_memfd).
*/
-bool kvm_arch_supports_gmem_mmap(struct kvm *kvm)
+bool kvm_arch_supports_gmem_init_shared(struct kvm *kvm)
{
return !kvm_arch_has_private_mem(kvm);
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 19b8c4bebb9c..680ca838f018 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -729,7 +729,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
#endif
#ifdef CONFIG_KVM_GUEST_MEMFD
-bool kvm_arch_supports_gmem_mmap(struct kvm *kvm);
+bool kvm_arch_supports_gmem_init_shared(struct kvm *kvm);
+
+static inline u64 kvm_gmem_get_supported_flags(struct kvm *kvm)
+{
+ u64 flags = GUEST_MEMFD_FLAG_MMAP;
+
+ if (!kvm || kvm_arch_supports_gmem_init_shared(kvm))
+ flags |= GUEST_MEMFD_FLAG_INIT_SHARED;
+
+ return flags;
+}
#endif
#ifndef kvm_arch_has_readonly_mem
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index e10d2c71e78c..fbca8c0972da 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -485,7 +485,7 @@ static const struct inode_operations kvm_gmem_iops = {
.setattr = kvm_gmem_setattr,
};
-bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm)
+bool __weak kvm_arch_supports_gmem_init_shared(struct kvm *kvm)
{
return true;
}
@@ -549,13 +549,8 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args)
{
loff_t size = args->size;
u64 flags = args->flags;
- u64 valid_flags = 0;
- if (kvm_arch_supports_gmem_mmap(kvm))
- valid_flags |= GUEST_MEMFD_FLAG_MMAP |
- GUEST_MEMFD_FLAG_INIT_SHARED;
-
- if (flags & ~valid_flags)
+ if (flags & ~kvm_gmem_get_supported_flags(kvm))
return -EINVAL;
if (size <= 0 || !PAGE_ALIGNED(size))
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5f644ca54af3..b7a0ae2a7b20 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4929,11 +4929,7 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
case KVM_CAP_GUEST_MEMFD:
return 1;
case KVM_CAP_GUEST_MEMFD_FLAGS:
- if (!kvm || kvm_arch_supports_gmem_mmap(kvm))
- return GUEST_MEMFD_FLAG_MMAP |
- GUEST_MEMFD_FLAG_INIT_SHARED;
-
- return 0;
+ return kvm_gmem_get_supported_flags(kvm);
#endif
default:
break;
--
2.51.0.618.g983fd99d29-goog
next prev parent reply other threads:[~2025-10-03 23:26 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-03 23:25 [PATCH v2 00/13] KVM: guest_memfd: MMAP and related fixes Sean Christopherson
2025-10-03 23:25 ` [PATCH v2 01/13] KVM: Rework KVM_CAP_GUEST_MEMFD_MMAP into KVM_CAP_GUEST_MEMFD_FLAGS Sean Christopherson
2025-10-06 19:16 ` Ackerley Tng
2025-10-06 20:19 ` Sean Christopherson
2025-10-07 16:09 ` Ackerley Tng
2025-10-07 16:13 ` Sean Christopherson
2025-10-10 14:07 ` David Hildenbrand
2025-10-03 23:25 ` [PATCH v2 02/13] KVM: guest_memfd: Add INIT_SHARED flag, reject user page faults if not set Sean Christopherson
2025-10-07 16:14 ` Ackerley Tng
2025-10-10 14:08 ` David Hildenbrand
2025-10-03 23:25 ` [PATCH v2 03/13] KVM: guest_memfd: Invalidate SHARED GPAs if gmem supports INIT_SHARED Sean Christopherson
2025-10-07 16:31 ` Ackerley Tng
2025-10-10 14:09 ` David Hildenbrand
2025-10-03 23:25 ` [PATCH v2 04/13] KVM: Explicitly mark KVM_GUEST_MEMFD as depending on KVM_GENERIC_MMU_NOTIFIER Sean Christopherson
2025-10-10 14:10 ` David Hildenbrand
2025-10-03 23:25 ` Sean Christopherson [this message]
2025-10-07 16:43 ` [PATCH v2 05/13] KVM: guest_memfd: Allow mmap() on guest_memfd for x86 VMs with private memory Ackerley Tng
2025-10-10 14:11 ` David Hildenbrand
2025-10-03 23:25 ` [PATCH v2 06/13] KVM: selftests: Stash the host page size in a global in the guest_memfd test Sean Christopherson
2025-10-06 18:30 ` Ackerley Tng
2025-10-03 23:26 ` [PATCH v2 07/13] KVM: selftests: Create a new guest_memfd for each testcase Sean Christopherson
2025-10-06 18:29 ` Ackerley Tng
2025-10-07 22:54 ` Lisa Wang
2025-10-10 15:04 ` David Hildenbrand
2025-10-10 20:12 ` Sean Christopherson
2025-10-03 23:26 ` [PATCH v2 08/13] KVM: selftests: Add test coverage for guest_memfd without GUEST_MEMFD_FLAG_MMAP Sean Christopherson
2025-10-03 23:26 ` [PATCH v2 09/13] KVM: selftests: Add wrappers for mmap() and munmap() to assert success Sean Christopherson
2025-10-03 23:26 ` [PATCH v2 10/13] KVM: selftests: Isolate the guest_memfd Copy-on-Write negative testcase Sean Christopherson
2025-10-06 18:28 ` Ackerley Tng
2025-10-03 23:26 ` [PATCH v2 11/13] KVM: selftests: Add wrapper macro to handle and assert on expected SIGBUS Sean Christopherson
2025-10-06 18:21 ` Ackerley Tng
2025-10-07 21:16 ` Lisa Wang
2025-10-03 23:26 ` [PATCH v2 12/13] KVM: selftests: Verify that faulting in private guest_memfd memory fails Sean Christopherson
2025-10-06 18:26 ` Ackerley Tng
2025-10-03 23:26 ` [PATCH v2 13/13] KVM: selftests: Verify that reads to inaccessible guest_memfd VMAs SIGBUS Sean Christopherson
2025-10-06 18:22 ` Ackerley Tng
2025-10-06 19:24 ` Sean Christopherson
2025-10-07 18:06 ` Lisa Wang
2025-10-10 21:30 ` [PATCH v2 00/13] KVM: guest_memfd: MMAP and related fixes Sean Christopherson
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