Update KVM's documentation to call out that KVM_EXIT_HYPERCALL requires
userspace to do KVM_RUN before state save/restore, so that KVM can skip
the hypercall instruction, otherwise resuming the vCPU after restore will
restart the instruction and potentially lead to a spurious MAP_GPA_RANGE.
Fixes: 0dbb11230437 ("KVM: X86: Introduce KVM_HC_MAP_GPA_RANGE hypercall")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 39 +++++++++++++++++-----------------
1 file changed, 20 insertions(+), 19 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 454c2aaa155e..c92c8d4e8779 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6615,13 +6615,29 @@ The 'data' member contains, in its first 'len' bytes, the value as it would
appear if the VCPU performed a load or store of the appropriate width directly
to the byte array.
+It is strongly recommended that userspace use ``KVM_EXIT_IO`` (x86) or
+``KVM_EXIT_MMIO`` (all except s390) to implement functionality that
+requires a guest to interact with host userspace.
+
+.. note:: KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO.
+
+ /* KVM_EXIT_HYPERCALL */
+ struct {
+ __u64 nr;
+ __u64 args[6];
+ __u64 ret;
+ __u64 flags;
+ } hypercall;
+
+
.. note::
For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR, KVM_EXIT_XEN,
- KVM_EXIT_EPR, KVM_EXIT_X86_RDMSR and KVM_EXIT_X86_WRMSR the corresponding
- operations are complete (and guest state is consistent) only after userspace
- has re-entered the kernel with KVM_RUN. The kernel side will first finish
- incomplete operations and then check for pending signals.
+ KVM_EXIT_EPR, KVM_EXIT_X86_RDMSR, KVM_EXIT_X86_WRMSR, and KVM_EXIT_HYPERCALL
+ the corresponding operations are complete (and guest state is consistent)
+ only after userspace has re-entered the kernel with KVM_RUN. The kernel
+ side will first finish incomplete operations and then check for pending
+ signals.
The pending state of the operation is not preserved in state which is
visible to userspace, thus userspace should ensure that the operation is
@@ -6632,21 +6648,6 @@ to the byte array.
::
- /* KVM_EXIT_HYPERCALL */
- struct {
- __u64 nr;
- __u64 args[6];
- __u64 ret;
- __u64 flags;
- } hypercall;
-
-
-It is strongly recommended that userspace use ``KVM_EXIT_IO`` (x86) or
-``KVM_EXIT_MMIO`` (all except s390) to implement functionality that
-requires a guest to interact with host userspace.
-
-.. note:: KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO.
-
For arm64:
----------
--
2.47.1.613.gc27f4b7a9f-goog
