* [PATCH v2 1/3] KVM: guest_memfd: Return -EEXIST for overlapping bindings
2026-05-22 17:21 [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest Sean Christopherson
@ 2026-05-22 17:21 ` Sean Christopherson
2026-05-22 17:21 ` [PATCH v2 2/3] KVM: selftests: Test guest_memfd binding overlap without GPA overlap Sean Christopherson
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Sean Christopherson @ 2026-05-22 17:21 UTC (permalink / raw)
To: Paolo Bonzini
Cc: kvm, linux-kernel, Zongyao Chen, Ackerley Tng, Sean Christopherson
From: Zongyao Chen <ZongYao.Chen@linux.alibaba.com>
KVM_SET_USER_MEMORY_REGION2 rejects guest_memfd ranges that overlap an
existing binding, but kvm_gmem_bind() currently reports the failure through
its generic -EINVAL path. That makes binding conflicts indistinguishable
from malformed guest_memfd parameters.
Return -EEXIST when the target guest_memfd range is already bound, matching
the errno used for overlapping GPA memslots and making the two types of
range conflicts report the same class of error to userspace.
Note, returning -EINVAL was definitely not intentional, as guest_memfd
support was accompanied by a selftest to verify that attempting to create
overlapping bindings fails with -EEXIST. Except the selftest was also
flawed in that it unintentionally overlapped memslot GPAs, and so failed
on KVM's common memslot checks before reaching guest_memfd.
Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
Signed-off-by: Zongyao Chen <ZongYao.Chen@linux.alibaba.com>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Ackerley Tng <ackerleytng@google.com>
[sean: call out that the original intent was to return -EEXIST]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
virt/kvm/guest_memfd.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 69c9d6d546b2..46727539d08a 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -675,6 +675,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
if (!xa_empty(&f->bindings) &&
xa_find(&f->bindings, &start, end - 1, XA_PRESENT)) {
+ r = -EEXIST;
filemap_invalidate_unlock(inode->i_mapping);
goto err;
}
--
2.54.0.794.g4f17f83d09-goog
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH v2 2/3] KVM: selftests: Test guest_memfd binding overlap without GPA overlap
2026-05-22 17:21 [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest Sean Christopherson
2026-05-22 17:21 ` [PATCH v2 1/3] KVM: guest_memfd: Return -EEXIST for overlapping bindings Sean Christopherson
@ 2026-05-22 17:21 ` Sean Christopherson
2026-05-22 17:21 ` [PATCH v2 3/3] KVM: selftests: Remove unnecessary "%s" formatting of a constant string Sean Christopherson
2026-05-27 18:10 ` [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest Sean Christopherson
3 siblings, 0 replies; 6+ messages in thread
From: Sean Christopherson @ 2026-05-22 17:21 UTC (permalink / raw)
To: Paolo Bonzini
Cc: kvm, linux-kernel, Zongyao Chen, Ackerley Tng, Sean Christopherson
From: Zongyao Chen <ZongYao.Chen@linux.alibaba.com>
The guest_memfd binding overlap test recreates the deleted slot with GPA
ranges that overlap the still-live slot. KVM rejects those attempts from
the generic memslot overlap check before reaching kvm_gmem_bind(), so the
test can pass even if guest_memfd binding overlap detection is broken.
Recreate the slot at its original, non-overlapping GPA and use guest_memfd
offsets that overlap the front and back halves of the other slot's binding.
Expand the guest_memfd so the back-half case remains within the file size.
Fixes: 2feabb855df8 ("KVM: selftests: Expand set_memory_region_test to validate guest_memfd()")
Signed-off-by: Zongyao Chen <ZongYao.Chen@linux.alibaba.com>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Ackerley Tng <ackerleytng@google.com>
[sean: keep the existing GPA overlap testcases]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
.../selftests/kvm/set_memory_region_test.c | 27 +++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
index 9b919a231c93..be99c1ff5a5a 100644
--- a/tools/testing/selftests/kvm/set_memory_region_test.c
+++ b/tools/testing/selftests/kvm/set_memory_region_test.c
@@ -510,7 +510,7 @@ static void test_add_overlapping_private_memory_regions(void)
vm = vm_create_barebones_type(KVM_X86_SW_PROTECTED_VM);
- memfd = vm_create_guest_memfd(vm, MEM_REGION_SIZE * 4, 0);
+ memfd = vm_create_guest_memfd(vm, MEM_REGION_SIZE * 5, 0);
vm_set_user_memory_region2(vm, MEM_REGION_SLOT, KVM_MEM_GUEST_MEMFD,
MEM_REGION_GPA, MEM_REGION_SIZE * 2, 0, memfd, 0);
@@ -526,7 +526,30 @@ static void test_add_overlapping_private_memory_regions(void)
vm_set_user_memory_region2(vm, MEM_REGION_SLOT, KVM_MEM_GUEST_MEMFD,
MEM_REGION_GPA, 0, NULL, -1, 0);
- /* Overlap the front half of the other slot. */
+ /*
+ * Verify that overlap in the guest_memfd bindings (i.e. in guest_memfd
+ * file offsets), but _not_ in the GPA space, fails with -EEXIST.
+ */
+ r = __vm_set_user_memory_region2(vm, MEM_REGION_SLOT, KVM_MEM_GUEST_MEMFD,
+ MEM_REGION_GPA,
+ MEM_REGION_SIZE * 2,
+ 0, memfd, MEM_REGION_SIZE);
+ TEST_ASSERT(r == -1 && errno == EEXIST,
+ "Overlapping guest_memfd() bindings should fail with EEXIST");
+
+ /* And now the back half of the other slot's guest_memfd binding. */
+ r = __vm_set_user_memory_region2(vm, MEM_REGION_SLOT, KVM_MEM_GUEST_MEMFD,
+ MEM_REGION_GPA,
+ MEM_REGION_SIZE * 2,
+ 0, memfd, MEM_REGION_SIZE * 3);
+ TEST_ASSERT(r == -1 && errno == EEXIST,
+ "Overlapping guest_memfd() bindings should fail with EEXIST");
+
+ /*
+ * Repeat the overlap tests, but this time with overlap in the memslots
+ * GPA space. Regardless of where there is overlap, KVM should return
+ * -EEXIST.
+ */
r = __vm_set_user_memory_region2(vm, MEM_REGION_SLOT, KVM_MEM_GUEST_MEMFD,
MEM_REGION_GPA * 2 - MEM_REGION_SIZE,
MEM_REGION_SIZE * 2,
--
2.54.0.794.g4f17f83d09-goog
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH v2 3/3] KVM: selftests: Remove unnecessary "%s" formatting of a constant string
2026-05-22 17:21 [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest Sean Christopherson
2026-05-22 17:21 ` [PATCH v2 1/3] KVM: guest_memfd: Return -EEXIST for overlapping bindings Sean Christopherson
2026-05-22 17:21 ` [PATCH v2 2/3] KVM: selftests: Test guest_memfd binding overlap without GPA overlap Sean Christopherson
@ 2026-05-22 17:21 ` Sean Christopherson
2026-05-22 17:52 ` Ackerley Tng
2026-05-27 18:10 ` [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest Sean Christopherson
3 siblings, 1 reply; 6+ messages in thread
From: Sean Christopherson @ 2026-05-22 17:21 UTC (permalink / raw)
To: Paolo Bonzini
Cc: kvm, linux-kernel, Zongyao Chen, Ackerley Tng, Sean Christopherson
Drop superfluous %s formatting from assertions in the guest_memfd overlap
testcases, as the string being printed doesn't require runtime formatting.
No functional change intended.
Reported-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
tools/testing/selftests/kvm/set_memory_region_test.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
index be99c1ff5a5a..e0800bfb11eb 100644
--- a/tools/testing/selftests/kvm/set_memory_region_test.c
+++ b/tools/testing/selftests/kvm/set_memory_region_test.c
@@ -554,7 +554,7 @@ static void test_add_overlapping_private_memory_regions(void)
MEM_REGION_GPA * 2 - MEM_REGION_SIZE,
MEM_REGION_SIZE * 2,
0, memfd, 0);
- TEST_ASSERT(r == -1 && errno == EEXIST, "%s",
+ TEST_ASSERT(r == -1 && errno == EEXIST,
"Overlapping guest_memfd() bindings should fail with EEXIST");
/* And now the back half of the other slot. */
@@ -562,7 +562,7 @@ static void test_add_overlapping_private_memory_regions(void)
MEM_REGION_GPA * 2 + MEM_REGION_SIZE,
MEM_REGION_SIZE * 2,
0, memfd, 0);
- TEST_ASSERT(r == -1 && errno == EEXIST, "%s",
+ TEST_ASSERT(r == -1 && errno == EEXIST,
"Overlapping guest_memfd() bindings should fail with EEXIST");
close(memfd);
--
2.54.0.794.g4f17f83d09-goog
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2 3/3] KVM: selftests: Remove unnecessary "%s" formatting of a constant string
2026-05-22 17:21 ` [PATCH v2 3/3] KVM: selftests: Remove unnecessary "%s" formatting of a constant string Sean Christopherson
@ 2026-05-22 17:52 ` Ackerley Tng
0 siblings, 0 replies; 6+ messages in thread
From: Ackerley Tng @ 2026-05-22 17:52 UTC (permalink / raw)
To: Sean Christopherson, Paolo Bonzini; +Cc: kvm, linux-kernel, Zongyao Chen
Sean Christopherson <seanjc@google.com> writes:
> Drop superfluous %s formatting from assertions in the guest_memfd overlap
> testcases, as the string being printed doesn't require runtime formatting.
>
> No functional change intended.
>
> Reported-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> tools/testing/selftests/kvm/set_memory_region_test.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> index be99c1ff5a5a..e0800bfb11eb 100644
> --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> @@ -554,7 +554,7 @@ static void test_add_overlapping_private_memory_regions(void)
> MEM_REGION_GPA * 2 - MEM_REGION_SIZE,
> MEM_REGION_SIZE * 2,
> 0, memfd, 0);
> - TEST_ASSERT(r == -1 && errno == EEXIST, "%s",
> + TEST_ASSERT(r == -1 && errno == EEXIST,
> "Overlapping guest_memfd() bindings should fail with EEXIST");
>
> /* And now the back half of the other slot. */
> @@ -562,7 +562,7 @@ static void test_add_overlapping_private_memory_regions(void)
> MEM_REGION_GPA * 2 + MEM_REGION_SIZE,
> MEM_REGION_SIZE * 2,
> 0, memfd, 0);
> - TEST_ASSERT(r == -1 && errno == EEXIST, "%s",
> + TEST_ASSERT(r == -1 && errno == EEXIST,
> "Overlapping guest_memfd() bindings should fail with EEXIST");
>
> close(memfd);
> --
> 2.54.0.794.g4f17f83d09-goog
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Thanks!
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest
2026-05-22 17:21 [PATCH v2 0/3] KVM: Fix guest_memfd binding overlap errno and selftest Sean Christopherson
` (2 preceding siblings ...)
2026-05-22 17:21 ` [PATCH v2 3/3] KVM: selftests: Remove unnecessary "%s" formatting of a constant string Sean Christopherson
@ 2026-05-27 18:10 ` Sean Christopherson
3 siblings, 0 replies; 6+ messages in thread
From: Sean Christopherson @ 2026-05-27 18:10 UTC (permalink / raw)
To: Sean Christopherson, Paolo Bonzini
Cc: kvm, linux-kernel, Zongyao Chen, Ackerley Tng
On Fri, 22 May 2026 10:21:48 -0700, Sean Christopherson wrote:
> Fix a goof where KVM rejects guest_memfd bindings that overlap an existing
> binding with EINVAL instead of the intended EEXIST, and then add that specific
> scenario to testcase that's supposed to verify overlap checks.
>
> v2:
> - Collect Ackerley's reviews.
> - Keep the GPA overlap testcases (because why not). [Sean]
> - Add a patch to remove superfluous %s formatting. [Ackerley]
>
> [...]
Applied to kvm-x86 gmem, thanks!
[1/3] KVM: guest_memfd: Return -EEXIST for overlapping bindings
https://github.com/kvm-x86/linux/commit/7ea987a90585
[2/3] KVM: selftests: Test guest_memfd binding overlap without GPA overlap
https://github.com/kvm-x86/linux/commit/772989854acd
[3/3] KVM: selftests: Remove unnecessary "%s" formatting of a constant string
https://github.com/kvm-x86/linux/commit/b0e476eb755e
--
https://github.com/kvm-x86/linux/tree/next
^ permalink raw reply [flat|nested] 6+ messages in thread