[kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Nadav Amit]

The test that checks the maximum VMCS field encoding does not probe all
possible VMCS fields. As a result it might fail since the actual
IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.

Change the test to check that the maximum of the supported probed
VMCS fields is lower/equal than the actual reported
IA32_VMX_VMCS_ENUM.MAX_INDEX.

This test might still fail on bare-metal due to errata (e.g., BDX30).

Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
---
 x86/vmx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/x86/vmx.c b/x86/vmx.c
index 962ec0f..f540e15 100644
--- a/x86/vmx.c
+++ b/x86/vmx.c
@@ -361,8 +361,8 @@ static void test_vmwrite_vmread(void)
 	report("VMWRITE/VMREAD", __check_all_vmcs_fields(0x42, &max_index));
 
 	vmcs_enum_max = rdmsr(MSR_IA32_VMX_VMCS_ENUM) & VMCS_FIELD_INDEX_MASK;
-	report("VMX_VMCS_ENUM.MAX_INDEX expected: %x, actual: %x",
-		vmcs_enum_max == max_index, max_index, vmcs_enum_max);
+	report("VMX_VMCS_ENUM.MAX_INDEX expected at least: %x, actual: %x",
+		vmcs_enum_max >= max_index, max_index, vmcs_enum_max);
 
 	assert(!vmcs_clear(vmcs));
 	free_page(vmcs);
-- 
2.17.1

Re: [kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Paolo Bonzini]

On 18/05/19 18:37, Nadav Amit wrote:
> The test that checks the maximum VMCS field encoding does not probe all
> possible VMCS fields. As a result it might fail since the actual
> IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.
> 
> Change the test to check that the maximum of the supported probed
> VMCS fields is lower/equal than the actual reported
> IA32_VMX_VMCS_ENUM.MAX_INDEX.
> 
> This test might still fail on bare-metal due to errata (e.g., BDX30).
> 
> Cc: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
> ---
>  x86/vmx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/x86/vmx.c b/x86/vmx.c
> index 962ec0f..f540e15 100644
> --- a/x86/vmx.c
> +++ b/x86/vmx.c
> @@ -361,8 +361,8 @@ static void test_vmwrite_vmread(void)
>  	report("VMWRITE/VMREAD", __check_all_vmcs_fields(0x42, &max_index));
>  
>  	vmcs_enum_max = rdmsr(MSR_IA32_VMX_VMCS_ENUM) & VMCS_FIELD_INDEX_MASK;
> -	report("VMX_VMCS_ENUM.MAX_INDEX expected: %x, actual: %x",
> -		vmcs_enum_max == max_index, max_index, vmcs_enum_max);
> +	report("VMX_VMCS_ENUM.MAX_INDEX expected at least: %x, actual: %x",
> +		vmcs_enum_max >= max_index, max_index, vmcs_enum_max);
>  
>  	assert(!vmcs_clear(vmcs));
>  	free_page(vmcs);
> 

Queued, thanks.

Paolo

Re: [kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Jim Mattson]

On Sat, May 18, 2019 at 4:58 PM Nadav Amit <nadav.amit@gmail.com> wrote:
>
> The test that checks the maximum VMCS field encoding does not probe all
> possible VMCS fields. As a result it might fail since the actual
> IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.
>
> Change the test to check that the maximum of the supported probed
> VMCS fields is lower/equal than the actual reported
> IA32_VMX_VMCS_ENUM.MAX_INDEX.

Wouldn't it be better to probe all possible VMCS fields and keep the
test for equality?

Re: [kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Nadav Amit]

> On Dec 13, 2019, at 12:59 AM, Jim Mattson <jmattson@google.com> wrote:
> 
> On Sat, May 18, 2019 at 4:58 PM Nadav Amit <nadav.amit@gmail.com> wrote:
>> The test that checks the maximum VMCS field encoding does not probe all
>> possible VMCS fields. As a result it might fail since the actual
>> IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.
>> 
>> Change the test to check that the maximum of the supported probed
>> VMCS fields is lower/equal than the actual reported
>> IA32_VMX_VMCS_ENUM.MAX_INDEX.
> 
> Wouldn't it be better to probe all possible VMCS fields and keep the
> test for equality?

It might take a while though…

How about probing VMREAD/VMWRITE to MAX_INDEX in addition to all the known
VMCS fields and then checking for equation?

Re: [kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Jim Mattson]

It can't take that long. VMCS field encodings are only 15 bits, and
you can ignore the "high" part of 64-bit fields, so that leaves only
14 bits.

On Fri, Dec 13, 2019 at 1:13 AM Nadav Amit <nadav.amit@gmail.com> wrote:
>
> > On Dec 13, 2019, at 12:59 AM, Jim Mattson <jmattson@google.com> wrote:
> >
> > On Sat, May 18, 2019 at 4:58 PM Nadav Amit <nadav.amit@gmail.com> wrote:
> >> The test that checks the maximum VMCS field encoding does not probe all
> >> possible VMCS fields. As a result it might fail since the actual
> >> IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.
> >>
> >> Change the test to check that the maximum of the supported probed
> >> VMCS fields is lower/equal than the actual reported
> >> IA32_VMX_VMCS_ENUM.MAX_INDEX.
> >
> > Wouldn't it be better to probe all possible VMCS fields and keep the
> > test for equality?
>
> It might take a while though…
>
> How about probing VMREAD/VMWRITE to MAX_INDEX in addition to all the known
> VMCS fields and then checking for equation?
>

Re: [kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Sean Christopherson]

On Fri, Dec 13, 2019 at 09:30:45AM -0800, Jim Mattson wrote:
> On Fri, Dec 13, 2019 at 1:13 AM Nadav Amit <nadav.amit@gmail.com> wrote:
> >
> > > On Dec 13, 2019, at 12:59 AM, Jim Mattson <jmattson@google.com> wrote:
> > >
> > > On Sat, May 18, 2019 at 4:58 PM Nadav Amit <nadav.amit@gmail.com> wrote:
> > >> The test that checks the maximum VMCS field encoding does not probe all
> > >> possible VMCS fields. As a result it might fail since the actual
> > >> IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.
> > >>
> > >> Change the test to check that the maximum of the supported probed
> > >> VMCS fields is lower/equal than the actual reported
> > >> IA32_VMX_VMCS_ENUM.MAX_INDEX.
> > >
> > > Wouldn't it be better to probe all possible VMCS fields and keep the
> > > test for equality?
> >
> > It might take a while though…
> >
> > How about probing VMREAD/VMWRITE to MAX_INDEX in addition to all the known
> > VMCS fields and then checking for equation?
> >
> It can't take that long. VMCS field encodings are only 15 bits, and
> you can ignore the "high" part of 64-bit fields, so that leaves only
> 14 bits.

Unless kvm-unit-tests is being run in L1, in which case things like this
are painful.  That being said, I do agree that probing "all" VMCS fields
is the way to go.  Walking from highest->lowest probably won't even take
all that many VMREADS.  If it is slow, the test can be binned to its own
config.

Re: [kvm-unit-tests PATCH] x86: Fix max VMCS field encoding index check

[Nadav Amit]

> On Dec 18, 2019, at 2:24 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> 
> On Fri, Dec 13, 2019 at 09:30:45AM -0800, Jim Mattson wrote:
>> On Fri, Dec 13, 2019 at 1:13 AM Nadav Amit <nadav.amit@gmail.com> wrote:
>>>> On Dec 13, 2019, at 12:59 AM, Jim Mattson <jmattson@google.com> wrote:
>>>> 
>>>> On Sat, May 18, 2019 at 4:58 PM Nadav Amit <nadav.amit@gmail.com> wrote:
>>>>> The test that checks the maximum VMCS field encoding does not probe all
>>>>> possible VMCS fields. As a result it might fail since the actual
>>>>> IA32_VMX_VMCS_ENUM.MAX_INDEX would be higher than the expected value.
>>>>> 
>>>>> Change the test to check that the maximum of the supported probed
>>>>> VMCS fields is lower/equal than the actual reported
>>>>> IA32_VMX_VMCS_ENUM.MAX_INDEX.
>>>> 
>>>> Wouldn't it be better to probe all possible VMCS fields and keep the
>>>> test for equality?
>>> 
>>> It might take a while though…
>>> 
>>> How about probing VMREAD/VMWRITE to MAX_INDEX in addition to all the known
>>> VMCS fields and then checking for equation?
>> It can't take that long. VMCS field encodings are only 15 bits, and
>> you can ignore the "high" part of 64-bit fields, so that leaves only
>> 14 bits.
> 
> Unless kvm-unit-tests is being run in L1, in which case things like this
> are painful.  That being said, I do agree that probing "all" VMCS fields
> is the way to go.  Walking from highest->lowest probably won't even take
> all that many VMREADS.  If it is slow, the test can be binned to its own
> config.

Ok. I’ll send a patch for that.