On 08.10.19 11:36, Christoffer Dall wrote:
In some scenarios, such as buggy guest or incorrect configuration of the
VMM and firmware description data, userspace will detect a memory access
to a portion of the IPA, which is not mapped to any MMIO region.
For this purpose, the appropriate action is to inject an external abort
to the guest. The kernel already has functionality to inject an
external abort, but we need to wire up a signal from user space that
lets user space tell the kernel to do this.
It turns out, we already have the set event functionality which we can
perfectly reuse for this.
Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxx>
---
Documentation/virt/kvm/api.txt | 18 +++++++++++++++++-
arch/arm/include/uapi/asm/kvm.h | 3 ++-
arch/arm/kvm/guest.c | 3 +++
arch/arm64/include/uapi/asm/kvm.h | 3 ++-
arch/arm64/kvm/guest.c | 3 +++
arch/arm64/kvm/inject_fault.c | 4 ++--
include/uapi/linux/kvm.h | 1 +
virt/kvm/arm/arm.c | 1 +
8 files changed, 31 insertions(+), 5 deletions(-)
diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
index 7403f15657c2..10ebe8cfda29 100644
--- a/Documentation/virt/kvm/api.txt
+++ b/Documentation/virt/kvm/api.txt
@@ -968,6 +968,8 @@ The following bits are defined in the flags field:
ARM/ARM64:
+User space may need to inject several types of events to the guest.
+
If the guest accesses a device that is being emulated by the host kernel in
such a way that a real device would generate a physical SError, KVM may make
a virtual SError pending for that VCPU. This system error interrupt remains
@@ -1002,12 +1004,26 @@ Specifying exception.has_esr on a system that does not support it will return
-EINVAL. Setting anything other than the lower 24bits of exception.serror_esr
will return -EINVAL.
+If the guest performed an access to I/O memory which could not be handled by
+userspace, for example because of missing instruction syndrome decode
+information or because there is no device mapped at the accessed IPA, then
+userspace can ask the kernel to inject an external abort using the address
+from the exiting fault on the VCPU. It is a programming error to set
+ext_dabt_pending at the same time as any of the serror fields, or to set
+ext_dabt_pending after an exit which was not either KVM_EXIT_MMIO or
+KVM_EXIT_ARM_NISV. This feature is only available if the system supports
+KVM_CAP_ARM_INJECT_EXT_DABT. This is a helper which provides commonality in
+how userspace reports accesses for the above cases to guests, across different
+userspace implementations. Nevertheless, userspace can still emulate all Arm
+exceptions by manipulating individual registers using the KVM_SET_ONE_REG API.
+
struct kvm_vcpu_events {
struct {
__u8 serror_pending;
__u8 serror_has_esr;
+ __u8 ext_dabt_pending;
/* Align it to 8 bytes */
- __u8 pad[6];
+ __u8 pad[5];
__u64 serror_esr;
} exception;
__u32 reserved[12];
diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
index 2769360f195c..03cd7c19a683 100644
--- a/arch/arm/include/uapi/asm/kvm.h
+++ b/arch/arm/include/uapi/asm/kvm.h
@@ -131,8 +131,9 @@ struct kvm_vcpu_events {
struct {
__u8 serror_pending;
__u8 serror_has_esr;
+ __u8 ext_dabt_pending;
/* Align it to 8 bytes */
- __u8 pad[6];
+ __u8 pad[5];
__u64 serror_esr;
} exception;
__u32 reserved[12];
diff --git a/arch/arm/kvm/guest.c b/arch/arm/kvm/guest.c
index 684cf64b4033..4154c5589501 100644
--- a/arch/arm/kvm/guest.c
+++ b/arch/arm/kvm/guest.c
@@ -263,11 +263,14 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu,
{
bool serror_pending = events->exception.serror_pending;
bool has_esr = events->exception.serror_has_esr;
+ bool has_ext_dabt_pending = events->exception.ext_dabt_pending;
if (serror_pending && has_esr)
return -EINVAL;
else if (serror_pending)
kvm_inject_vabt(vcpu);
+ else if (has_ext_dabt_pending)
+ kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
return 0;
}
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 67c21f9bdbad..d49c17a80491 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -164,8 +164,9 @@ struct kvm_vcpu_events {
struct {
__u8 serror_pending;
__u8 serror_has_esr;
+ __u8 ext_dabt_pending;
/* Align it to 8 bytes */
- __u8 pad[6];
+ __u8 pad[5];
__u64 serror_esr;
} exception;
__u32 reserved[12];
diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index dfd626447482..10e6e2144dca 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -720,6 +720,7 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu,
{
bool serror_pending = events->exception.serror_pending;
bool has_esr = events->exception.serror_has_esr;
+ bool has_ext_dabt_pending = events->exception.ext_dabt_pending;
The has_ is inconsistent here (and below in the copies of this function).
What I'm really curious on is why it's written the way it is though. Why
not just make "exception" be a named struct and refer to a pointer of
that here?
struct kvm_arm_exception *e = &events->exception;
if (e->serror_pending && e->serror_has_esr) {
...
} else if (e->ext_dabt_pending) {
...
}
Copying the values into their own local bools looks a bit convoluted to
me. In fact, why do we copy u8s into bools in the first place?
if (serror_pending && has_esr) {
if (!cpus_have_const_cap(ARM64_HAS_RAS_EXTN))
@@ -731,6 +732,8 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu,
return -EINVAL;
} else if (serror_pending) {
kvm_inject_vabt(vcpu);
+ } else if (has_ext_dabt_pending) {
+ kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
I'm a bit confused on the else if here. I understand that we probably
don't want to inject an serror at the same time as a dabt, but shouldn't
the API express that dependency?
Do we have guarantees on the value of "serror_pending"? Can we assume
it's always either 0 or 1 today given all known user space? Maybe we can
create a union and make this an "exception_pending" enum instead which
indicates which exception we want to inject?
Alex
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
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