[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <20250731205844.1346839-4-jiaqiyan@google.com>
Date: Thu, 31 Jul 2025 20:58:44 +0000
From: Jiaqi Yan <jiaqiyan@...gle.com>
To: maz@...nel.org, oliver.upton@...ux.dev
Cc: joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com,
catalin.marinas@....com, will@...nel.org, pbonzini@...hat.com, corbet@....net,
shuah@...nel.org, kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
duenwen@...gle.com, rananta@...gle.com, jthoughton@...gle.com,
Jiaqi Yan <jiaqiyan@...gle.com>
Subject: [PATCH v3 3/3] Documentation: kvm: new UAPI for handling SEA
Document the new userspace-visible features and APIs for handling
synchronous external abort (SEA)
- KVM_CAP_ARM_SEA_TO_USER: How userspace enables the new feature.
- KVM_EXIT_ARM_SEA: exit userspace gets when it needs to handle SEA
and what userspace gets while taking the SEA.
Signed-off-by: Jiaqi Yan <jiaqiyan@...gle.com>
---
Documentation/virt/kvm/api.rst | 61 ++++++++++++++++++++++++++++++++++
1 file changed, 61 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 53e0179d52949..b61bca10a3a10 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7231,6 +7231,55 @@ exit, even without calls to ``KVM_ENABLE_CAP`` or similar. In this case,
it will enter with output fields already valid; in the common case, the
``unknown.ret`` field of the union will be ``TDVMCALL_STATUS_SUBFUNC_UNSUPPORTED``.
Userspace need not do anything if it does not wish to support a TDVMCALL.
+
+::
+ /* KVM_EXIT_ARM_SEA */
+ struct {
+ __u64 esr;
+ #define KVM_EXIT_ARM_SEA_FLAG_GPA_VALID (1ULL << 0)
+ __u64 flags;
+ __u64 gva;
+ __u64 gpa;
+ } arm_sea;
+
+Used on arm64 systems. When the VM capability KVM_CAP_ARM_SEA_TO_USER is
+enabled, a VM exit is generated if guest causes a synchronous external abort
+(SEA) and the host APEI fails to handle the SEA.
+
+Historically KVM handles SEA by first delegating the SEA to host APEI as there
+is high chance that the SEA is caused by consuming uncorrected memory error.
+However, not all platforms support SEA handling in APEI, and KVM's fallback
+handling is to inject an async SError into the guest, which usually panics
+guest kernel unpleasantly. As an alternative, userspace can participate in
+the SEA handling by enabling KVM_CAP_ARM_SEA_TO_USER at VM creation, after
+querying the capability. Once enabled, when KVM has to handle the guest
+caused SEA, it returns to userspace with KVM_EXIT_ARM_SEA, with details
+about the SEA available in 'arm_sea'.
+
+The 'esr' field holds the value of the exception syndrome register (ESR) while
+KVM taking the SEA, which tells userspace the character of the current SEA,
+such as its Exception Class, Synchronous Error Type, Fault Specific Code and
+so on. For more details on ESR, check the Arm Architecture Registers
+documentation.
+
+The following values are defined for the 'flags' field
+
+ - KVM_EXIT_ARM_SEA_FLAG_GPA_VALID -- the faulting guest physical address
+ is valid and userspace can get its value in the 'gpa' field.
+
+Note userspace can tell whether the faulting guest virtual address is valid
+from the FnV bit in 'esr' field. If FnV bit in 'esr' field is not set, the
+'gva' field holds the valid faulting guest virtual address.
+
+Userspace needs to take actions to handle guest SEA synchronously, namely in
+the same thread that runs KVM_RUN and receives KVM_EXIT_ARM_SEA. One of the
+encouraged approach is to utilize the KVM_SET_VCPU_EVENTS to inject the SEA
+to the faulting VCPU. This way, the guest has the opportunity to keep running
+and limit the blast radius of the SEA to the particular guest application that
+caused the SEA. Userspace may also emulate the SEA to VM by itself using the
+KVM_SET_ONE_REG API. In this case, it can use the valid values from 'gva' and
+'gpa' fields to manipulate VCPU's registers (e.g. FAR_EL1, HPFAR_EL1).
+
::
/* Fix the size of the union. */
@@ -8625,6 +8674,18 @@ 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.
+7.45 KVM_CAP_ARM_SEA_TO_USER
+----------------------------
+
+:Architecture: arm64
+:Target: VM
+:Parameters: none
+:Returns: 0 on success, -EINVAL if unsupported.
+
+This capability, if KVM_CHECK_EXTENSION indicates that it is available, means
+that KVM has an implementation that allows userspace to participate in handling
+synchronous external abort caused by VM, by an exit of KVM_EXIT_ARM_SEA.
+
8. Other capabilities.
======================
--
2.50.1.565.gc32cd1483b-goog
Powered by blists - more mailing lists