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* [PATCH] arm64: KVM: Only skip MMIO insn once
@ 2019-08-21 19:50 Andrew Jones
  2019-08-22  8:30 ` Marc Zyngier
  0 siblings, 1 reply; 5+ messages in thread
From: Andrew Jones @ 2019-08-21 19:50 UTC (permalink / raw)
  To: kvmarm, kvm; +Cc: maz, mark.rutland

If after an MMIO exit to userspace a VCPU is immediately run with an
immediate_exit request, such as when a signal is delivered or an MMIO
emulation completion is needed, then the VCPU completes the MMIO
emulation and immediately returns to userspace. As the exit_reason
does not get changed from KVM_EXIT_MMIO in these cases we have to
be careful not to complete the MMIO emulation again, when the VCPU is
eventually run again, because the emulation does an instruction skip
(and doing too many skips would be a waste of guest code :-) We need
to use additional VCPU state to track if the emulation is complete.
As luck would have it, we already have 'mmio_needed', which even
appears to be used in this way by other architectures already.

Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 virt/kvm/arm/arm.c  | 3 ++-
 virt/kvm/arm/mmio.c | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 35a069815baf..322cf9030bbe 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	if (ret)
 		return ret;
 
-	if (run->exit_reason == KVM_EXIT_MMIO) {
+	if (vcpu->mmio_needed) {
+		vcpu->mmio_needed = 0;
 		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
 		if (ret)
 			return ret;
diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
index a8a6a0c883f1..2d9b5e064ae0 100644
--- a/virt/kvm/arm/mmio.c
+++ b/virt/kvm/arm/mmio.c
@@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	if (is_write)
 		memcpy(run->mmio.data, data_buf, len);
 	vcpu->stat.mmio_exit_user++;
+	vcpu->mmio_needed	= 1;
 	run->exit_reason	= KVM_EXIT_MMIO;
 	return 0;
 }
-- 
2.18.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] arm64: KVM: Only skip MMIO insn once
  2019-08-21 19:50 [PATCH] arm64: KVM: Only skip MMIO insn once Andrew Jones
@ 2019-08-22  8:30 ` Marc Zyngier
  2019-08-22  9:25   ` Andrew Jones
  0 siblings, 1 reply; 5+ messages in thread
From: Marc Zyngier @ 2019-08-22  8:30 UTC (permalink / raw)
  To: Andrew Jones, kvmarm, kvm; +Cc: mark.rutland

Hi Drew,

On 21/08/2019 20:50, Andrew Jones wrote:
> If after an MMIO exit to userspace a VCPU is immediately run with an
> immediate_exit request, such as when a signal is delivered or an MMIO
> emulation completion is needed, then the VCPU completes the MMIO
> emulation and immediately returns to userspace. As the exit_reason
> does not get changed from KVM_EXIT_MMIO in these cases we have to
> be careful not to complete the MMIO emulation again, when the VCPU is
> eventually run again, because the emulation does an instruction skip
> (and doing too many skips would be a waste of guest code :-) We need
> to use additional VCPU state to track if the emulation is complete.
> As luck would have it, we already have 'mmio_needed', which even
> appears to be used in this way by other architectures already.
> 
> Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  virt/kvm/arm/arm.c  | 3 ++-
>  virt/kvm/arm/mmio.c | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 35a069815baf..322cf9030bbe 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	if (ret)
>  		return ret;
>  
> -	if (run->exit_reason == KVM_EXIT_MMIO) {
> +	if (vcpu->mmio_needed) {
> +		vcpu->mmio_needed = 0;
>  		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
>  		if (ret)
>  			return ret;
> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> index a8a6a0c883f1..2d9b5e064ae0 100644
> --- a/virt/kvm/arm/mmio.c
> +++ b/virt/kvm/arm/mmio.c
> @@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	if (is_write)
>  		memcpy(run->mmio.data, data_buf, len);
>  	vcpu->stat.mmio_exit_user++;
> +	vcpu->mmio_needed	= 1;
>  	run->exit_reason	= KVM_EXIT_MMIO;
>  	return 0;
>  }
> 

Thanks for this. That's quite embarrassing. Out of curiosity,
how was this spotted?

Patch wise, I'd have a small preference for the following (untested)
patch, as it keeps the mmio_needed accesses close together, making
it easier to read (at least for me). What do you think?

	M.

diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
index a8a6a0c883f1..6af5c91337f2 100644
--- a/virt/kvm/arm/mmio.c
+++ b/virt/kvm/arm/mmio.c
@@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	unsigned int len;
 	int mask;
 
+	/* Detect an already handled MMIO return */
+	if (unlikely(!vcpu->mmio_needed))
+		return 0;
+
+	vcpu->mmio_needed = 0;
+
 	if (!run->mmio.is_write) {
 		len = run->mmio.len;
 		if (len > sizeof(unsigned long))
@@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	run->mmio.is_write	= is_write;
 	run->mmio.phys_addr	= fault_ipa;
 	run->mmio.len		= len;
+	vcpu->mmio_needed	= 1;
 
 	if (!ret) {
 		/* We handled the access successfully in the kernel. */
-- 
Jazz is not dead, it just smells funny...

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] arm64: KVM: Only skip MMIO insn once
  2019-08-22  8:30 ` Marc Zyngier
@ 2019-08-22  9:25   ` Andrew Jones
  2019-08-22  9:38     ` Marc Zyngier
  0 siblings, 1 reply; 5+ messages in thread
From: Andrew Jones @ 2019-08-22  9:25 UTC (permalink / raw)
  To: Marc Zyngier; +Cc: kvmarm, kvm, mark.rutland

On Thu, Aug 22, 2019 at 09:30:44AM +0100, Marc Zyngier wrote:
> Hi Drew,
> 
> On 21/08/2019 20:50, Andrew Jones wrote:
> > If after an MMIO exit to userspace a VCPU is immediately run with an
> > immediate_exit request, such as when a signal is delivered or an MMIO
> > emulation completion is needed, then the VCPU completes the MMIO
> > emulation and immediately returns to userspace. As the exit_reason
> > does not get changed from KVM_EXIT_MMIO in these cases we have to
> > be careful not to complete the MMIO emulation again, when the VCPU is
> > eventually run again, because the emulation does an instruction skip
> > (and doing too many skips would be a waste of guest code :-) We need
> > to use additional VCPU state to track if the emulation is complete.
> > As luck would have it, we already have 'mmio_needed', which even
> > appears to be used in this way by other architectures already.
> > 
> > Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
> > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > ---
> >  virt/kvm/arm/arm.c  | 3 ++-
> >  virt/kvm/arm/mmio.c | 1 +
> >  2 files changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > index 35a069815baf..322cf9030bbe 100644
> > --- a/virt/kvm/arm/arm.c
> > +++ b/virt/kvm/arm/arm.c
> > @@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >  	if (ret)
> >  		return ret;
> >  
> > -	if (run->exit_reason == KVM_EXIT_MMIO) {
> > +	if (vcpu->mmio_needed) {
> > +		vcpu->mmio_needed = 0;
> >  		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
> >  		if (ret)
> >  			return ret;
> > diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> > index a8a6a0c883f1..2d9b5e064ae0 100644
> > --- a/virt/kvm/arm/mmio.c
> > +++ b/virt/kvm/arm/mmio.c
> > @@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
> >  	if (is_write)
> >  		memcpy(run->mmio.data, data_buf, len);
> >  	vcpu->stat.mmio_exit_user++;
> > +	vcpu->mmio_needed	= 1;
> >  	run->exit_reason	= KVM_EXIT_MMIO;
> >  	return 0;
> >  }
> > 
> 
> Thanks for this. That's quite embarrassing. Out of curiosity,
> how was this spotted?

avocado has a guest execution state snapshotting feature. The feature
simply periodically uses QEMU's 'info registers' monitor command while
a guest is running. The monitor command kicks the vcpu to userspace with
a signal, and since avocado's snapshot rate was set relatively high that
increased the probability of causing a noticeable (weird things / guest
crashes) event during guest boot (when MMIO activity is also high). The
signals correlated with guest crashes lead me to this code.

> 
> Patch wise, I'd have a small preference for the following (untested)
> patch, as it keeps the mmio_needed accesses close together, making
> it easier to read (at least for me). What do you think?
> 
> 	M.
> 
> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> index a8a6a0c883f1..6af5c91337f2 100644
> --- a/virt/kvm/arm/mmio.c
> +++ b/virt/kvm/arm/mmio.c
> @@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	unsigned int len;
>  	int mask;
>  
> +	/* Detect an already handled MMIO return */
> +	if (unlikely(!vcpu->mmio_needed))
> +		return 0;
> +
> +	vcpu->mmio_needed = 0;
> +
>  	if (!run->mmio.is_write) {
>  		len = run->mmio.len;
>  		if (len > sizeof(unsigned long))
> @@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	run->mmio.is_write	= is_write;
>  	run->mmio.phys_addr	= fault_ipa;
>  	run->mmio.len		= len;
> +	vcpu->mmio_needed	= 1;
>  
>  	if (!ret) {
>  		/* We handled the access successfully in the kernel. */

That looks good to me. Should I repost?

Thanks,
drew

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] arm64: KVM: Only skip MMIO insn once
  2019-08-22  9:25   ` Andrew Jones
@ 2019-08-22  9:38     ` Marc Zyngier
  2019-08-22 10:42       ` Andrew Jones
  0 siblings, 1 reply; 5+ messages in thread
From: Marc Zyngier @ 2019-08-22  9:38 UTC (permalink / raw)
  To: Andrew Jones; +Cc: kvmarm, kvm, mark.rutland

On 22/08/2019 10:25, Andrew Jones wrote:
> On Thu, Aug 22, 2019 at 09:30:44AM +0100, Marc Zyngier wrote:
>> Hi Drew,
>>
>> On 21/08/2019 20:50, Andrew Jones wrote:
>>> If after an MMIO exit to userspace a VCPU is immediately run with an
>>> immediate_exit request, such as when a signal is delivered or an MMIO
>>> emulation completion is needed, then the VCPU completes the MMIO
>>> emulation and immediately returns to userspace. As the exit_reason
>>> does not get changed from KVM_EXIT_MMIO in these cases we have to
>>> be careful not to complete the MMIO emulation again, when the VCPU is
>>> eventually run again, because the emulation does an instruction skip
>>> (and doing too many skips would be a waste of guest code :-) We need
>>> to use additional VCPU state to track if the emulation is complete.
>>> As luck would have it, we already have 'mmio_needed', which even
>>> appears to be used in this way by other architectures already.
>>>
>>> Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
>>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>>> ---
>>>  virt/kvm/arm/arm.c  | 3 ++-
>>>  virt/kvm/arm/mmio.c | 1 +
>>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>>> index 35a069815baf..322cf9030bbe 100644
>>> --- a/virt/kvm/arm/arm.c
>>> +++ b/virt/kvm/arm/arm.c
>>> @@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>>  	if (ret)
>>>  		return ret;
>>>  
>>> -	if (run->exit_reason == KVM_EXIT_MMIO) {
>>> +	if (vcpu->mmio_needed) {
>>> +		vcpu->mmio_needed = 0;
>>>  		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
>>>  		if (ret)
>>>  			return ret;
>>> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
>>> index a8a6a0c883f1..2d9b5e064ae0 100644
>>> --- a/virt/kvm/arm/mmio.c
>>> +++ b/virt/kvm/arm/mmio.c
>>> @@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>>  	if (is_write)
>>>  		memcpy(run->mmio.data, data_buf, len);
>>>  	vcpu->stat.mmio_exit_user++;
>>> +	vcpu->mmio_needed	= 1;
>>>  	run->exit_reason	= KVM_EXIT_MMIO;
>>>  	return 0;
>>>  }
>>>
>>
>> Thanks for this. That's quite embarrassing. Out of curiosity,
>> how was this spotted?
> 
> avocado has a guest execution state snapshotting feature. The feature
> simply periodically uses QEMU's 'info registers' monitor command while
> a guest is running. The monitor command kicks the vcpu to userspace with
> a signal, and since avocado's snapshot rate was set relatively high that
> increased the probability of causing a noticeable (weird things / guest
> crashes) event during guest boot (when MMIO activity is also high). The
> signals correlated with guest crashes lead me to this code.

Nice one. I guess I could try and reproduce it with the kvmtool debug
feature that does a similar thing.

>> Patch wise, I'd have a small preference for the following (untested)
>> patch, as it keeps the mmio_needed accesses close together, making
>> it easier to read (at least for me). What do you think?
>>
>> 	M.
>>
>> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
>> index a8a6a0c883f1..6af5c91337f2 100644
>> --- a/virt/kvm/arm/mmio.c
>> +++ b/virt/kvm/arm/mmio.c
>> @@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>  	unsigned int len;
>>  	int mask;
>>  
>> +	/* Detect an already handled MMIO return */
>> +	if (unlikely(!vcpu->mmio_needed))
>> +		return 0;
>> +
>> +	vcpu->mmio_needed = 0;
>> +
>>  	if (!run->mmio.is_write) {
>>  		len = run->mmio.len;
>>  		if (len > sizeof(unsigned long))
>> @@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  	run->mmio.is_write	= is_write;
>>  	run->mmio.phys_addr	= fault_ipa;
>>  	run->mmio.len		= len;
>> +	vcpu->mmio_needed	= 1;
>>  
>>  	if (!ret) {
>>  		/* We handled the access successfully in the kernel. */
> 
> That looks good to me. Should I repost?

Yes please. I'll try to get Paolo to pick it as quickly as possible.

Thanks,

	M.
-- 
Jazz is not dead, it just smells funny...

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] arm64: KVM: Only skip MMIO insn once
  2019-08-22  9:38     ` Marc Zyngier
@ 2019-08-22 10:42       ` Andrew Jones
  0 siblings, 0 replies; 5+ messages in thread
From: Andrew Jones @ 2019-08-22 10:42 UTC (permalink / raw)
  To: Marc Zyngier; +Cc: kvmarm, kvm, mark.rutland

On Thu, Aug 22, 2019 at 10:38:52AM +0100, Marc Zyngier wrote:
> On 22/08/2019 10:25, Andrew Jones wrote:
> > On Thu, Aug 22, 2019 at 09:30:44AM +0100, Marc Zyngier wrote:
> >> Hi Drew,
> >>
> >> On 21/08/2019 20:50, Andrew Jones wrote:
> >>> If after an MMIO exit to userspace a VCPU is immediately run with an
> >>> immediate_exit request, such as when a signal is delivered or an MMIO
> >>> emulation completion is needed, then the VCPU completes the MMIO
> >>> emulation and immediately returns to userspace. As the exit_reason
> >>> does not get changed from KVM_EXIT_MMIO in these cases we have to
> >>> be careful not to complete the MMIO emulation again, when the VCPU is
> >>> eventually run again, because the emulation does an instruction skip
> >>> (and doing too many skips would be a waste of guest code :-) We need
> >>> to use additional VCPU state to track if the emulation is complete.
> >>> As luck would have it, we already have 'mmio_needed', which even
> >>> appears to be used in this way by other architectures already.
> >>>
> >>> Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
> >>> Signed-off-by: Andrew Jones <drjones@redhat.com>
> >>> ---
> >>>  virt/kvm/arm/arm.c  | 3 ++-
> >>>  virt/kvm/arm/mmio.c | 1 +
> >>>  2 files changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> >>> index 35a069815baf..322cf9030bbe 100644
> >>> --- a/virt/kvm/arm/arm.c
> >>> +++ b/virt/kvm/arm/arm.c
> >>> @@ -669,7 +669,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >>>  	if (ret)
> >>>  		return ret;
> >>>  
> >>> -	if (run->exit_reason == KVM_EXIT_MMIO) {
> >>> +	if (vcpu->mmio_needed) {
> >>> +		vcpu->mmio_needed = 0;
> >>>  		ret = kvm_handle_mmio_return(vcpu, vcpu->run);
> >>>  		if (ret)
> >>>  			return ret;
> >>> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> >>> index a8a6a0c883f1..2d9b5e064ae0 100644
> >>> --- a/virt/kvm/arm/mmio.c
> >>> +++ b/virt/kvm/arm/mmio.c
> >>> @@ -201,6 +201,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
> >>>  	if (is_write)
> >>>  		memcpy(run->mmio.data, data_buf, len);
> >>>  	vcpu->stat.mmio_exit_user++;
> >>> +	vcpu->mmio_needed	= 1;
> >>>  	run->exit_reason	= KVM_EXIT_MMIO;
> >>>  	return 0;
> >>>  }
> >>>
> >>
> >> Thanks for this. That's quite embarrassing. Out of curiosity,
> >> how was this spotted?
> > 
> > avocado has a guest execution state snapshotting feature. The feature
> > simply periodically uses QEMU's 'info registers' monitor command while
> > a guest is running. The monitor command kicks the vcpu to userspace with
> > a signal, and since avocado's snapshot rate was set relatively high that
> > increased the probability of causing a noticeable (weird things / guest
> > crashes) event during guest boot (when MMIO activity is also high). The
> > signals correlated with guest crashes lead me to this code.
> 
> Nice one. I guess I could try and reproduce it with the kvmtool debug
> feature that does a similar thing.

Since we don't even need the signals, we can just use kselftests to send a
few KVM_RUN ioctls. Here's one

From: Andrew Jones <drjones@redhat.com>
Date: Thu, 22 Aug 2019 06:38:26 -0400
Subject: [PATCH] KVM: selftests: Demonstrate AArch64 extra instruction skip

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 tools/testing/selftests/kvm/Makefile          |  1 +
 .../testing/selftests/kvm/aarch64/vcpu-skip.c | 40 +++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/aarch64/vcpu-skip.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index ba7849751989..1b90b99bc351 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -28,6 +28,7 @@ TEST_GEN_PROGS_x86_64 += clear_dirty_log_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test
 TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus
 
+TEST_GEN_PROGS_aarch64 += aarch64/vcpu-skip
 TEST_GEN_PROGS_aarch64 += clear_dirty_log_test
 TEST_GEN_PROGS_aarch64 += dirty_log_test
 TEST_GEN_PROGS_aarch64 += kvm_create_max_vcpus
diff --git a/tools/testing/selftests/kvm/aarch64/vcpu-skip.c b/tools/testing/selftests/kvm/aarch64/vcpu-skip.c
new file mode 100644
index 000000000000..f3a747739d36
--- /dev/null
+++ b/tools/testing/selftests/kvm/aarch64/vcpu-skip.c
@@ -0,0 +1,40 @@
+#include "kvm_util.h"
+#include "../lib/kvm_util_internal.h"
+
+#define MMIO 0xb000000
+
+static uint64_t result;
+
+static void guest_code(void)
+{
+	asm volatile(
+		"mov	x0, #1\n"
+		"str	x0, [%0]\n"
+		"str	x0, [%1]\n"
+		"str	x0, [%0]\n"
+	: : "r" (MMIO), "r" (&result) : "x0");
+}
+
+int main(void)
+{
+	struct kvm_vm *vm;
+	struct kvm_run *run;
+	int fd;
+
+	vm = vm_create_default(1, 0, guest_code);
+	virt_pg_map(vm, MMIO, MMIO, 0);
+	run = vcpu_state(vm, 1);
+	fd = vcpu_find(vm, 1)->fd;
+
+	ioctl(fd, KVM_RUN, NULL);
+
+	run->immediate_exit = 1;
+	ioctl(fd, KVM_RUN, NULL);
+
+	run->immediate_exit = 0;
+	ioctl(fd, KVM_RUN, NULL);
+
+	sync_global_from_guest(vm, result);
+	TEST_ASSERT(result, "Skipped instruction");
+	return 0;
+}
-- 
2.18.1

> 
> >> Patch wise, I'd have a small preference for the following (untested)
> >> patch, as it keeps the mmio_needed accesses close together, making
> >> it easier to read (at least for me). What do you think?
> >>
> >> 	M.
> >>
> >> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> >> index a8a6a0c883f1..6af5c91337f2 100644
> >> --- a/virt/kvm/arm/mmio.c
> >> +++ b/virt/kvm/arm/mmio.c
> >> @@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >>  	unsigned int len;
> >>  	int mask;
> >>  
> >> +	/* Detect an already handled MMIO return */
> >> +	if (unlikely(!vcpu->mmio_needed))
> >> +		return 0;
> >> +
> >> +	vcpu->mmio_needed = 0;
> >> +
> >>  	if (!run->mmio.is_write) {
> >>  		len = run->mmio.len;
> >>  		if (len > sizeof(unsigned long))
> >> @@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
> >>  	run->mmio.is_write	= is_write;
> >>  	run->mmio.phys_addr	= fault_ipa;
> >>  	run->mmio.len		= len;
> >> +	vcpu->mmio_needed	= 1;
> >>  
> >>  	if (!ret) {
> >>  		/* We handled the access successfully in the kernel. */
> > 
> > That looks good to me. Should I repost?
> 
> Yes please. I'll try to get Paolo to pick it as quickly as possible.

On it's way

Thanks,
drew

^ permalink raw reply	[flat|nested] 5+ messages in thread

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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-21 19:50 [PATCH] arm64: KVM: Only skip MMIO insn once Andrew Jones
2019-08-22  8:30 ` Marc Zyngier
2019-08-22  9:25   ` Andrew Jones
2019-08-22  9:38     ` Marc Zyngier
2019-08-22 10:42       ` Andrew Jones

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