Commit da345174 authored by Christoffer Dall's avatar Christoffer Dall Committed by Marc Zyngier
Browse files

KVM: arm/arm64: Allow user injection of external data aborts 



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: default avatarChristoffer Dall <christoffer.dall@arm.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent c726200d

Documentation/virt/kvm/api.txt

+21 −1
Original line number Diff line number Diff line
@@ -1002,12 +1002,18 @@ 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.



It is not possible to read back a pending external abort (injected via

KVM_SET_VCPU_EVENTS or otherwise) because such an exception is always delivered

directly to the virtual CPU).





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];
@@ -1051,9 +1057,23 @@ contain a valid state and shall be written into the VCPU. 


ARM/ARM64:



User space may need to inject several types of events to the guest.



Set the pending SError exception state for this VCPU. It is not possible to

'cancel' an Serror that has been made pending.



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 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.



See KVM_GET_VCPU_EVENTS for the data structure.

arch/arm/include/uapi/asm/kvm.h

+2 −1
Original line number Diff line number Diff line
@@ -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];

arch/arm/kvm/guest.c

+10 −0
Original line number Diff line number Diff line
@@ -255,6 +255,12 @@ int __kvm_arm_vcpu_get_events(struct kvm_vcpu *vcpu, 
{

	events->exception.serror_pending = !!(*vcpu_hcr(vcpu) & HCR_VA);



	/*

	 * We never return a pending ext_dabt here because we deliver it to

	 * the virtual CPU directly when setting the event and it's no longer

	 * 'pending' at this point.

	 */



	return 0;

}
@@ -263,12 +269,16 @@ 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 ext_dabt_pending = events->exception.ext_dabt_pending;



	if (serror_pending && has_esr)

		return -EINVAL;

	else if (serror_pending)

		kvm_inject_vabt(vcpu);



	if (ext_dabt_pending)

		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));



	return 0;

}

arch/arm64/include/uapi/asm/kvm.h

+2 −1
Original line number Diff line number Diff line
@@ -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];

arch/arm64/kvm/guest.c

+10 −0
Original line number Diff line number Diff line
@@ -712,6 +712,12 @@ int __kvm_arm_vcpu_get_events(struct kvm_vcpu *vcpu, 
	if (events->exception.serror_pending && events->exception.serror_has_esr)

		events->exception.serror_esr = vcpu_get_vsesr(vcpu);



	/*

	 * We never return a pending ext_dabt here because we deliver it to

	 * the virtual CPU directly when setting the event and it's no longer

	 * 'pending' at this point.

	 */



	return 0;

}
@@ -720,6 +726,7 @@ 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 ext_dabt_pending = events->exception.ext_dabt_pending;



	if (serror_pending && has_esr) {

		if (!cpus_have_const_cap(ARM64_HAS_RAS_EXTN))
@@ -733,6 +740,9 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu, 
		kvm_inject_vabt(vcpu);

	}



	if (ext_dabt_pending)

		kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));



	return 0;

}

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