7a0 is an integer field, not a mask - taking the logical and of the hardware
and policy values results in nonsense. Instead, take the policy value
directly.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
Even Rome hardware has 7[0].eax still as 0, and there is no sensible reason to
set max_subleaf higher at this point, so this is only a latent bug for now.
---
xen/arch/x86/domctl.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 1e98fc8009..35ad8cb51c 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
{
uint64_t mask = cpuidmask_defaults._7ab0;
- uint32_t eax = ctl->eax;
- uint32_t ebx = p->feat._7b0;
- if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
- mask &= ((uint64_t)eax << 32) | ebx;
+ /*
+ * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
+ * wholesale from the policy, but clamp the features in 7[0].ebx
+ * per usual.
+ */
+ if ( boot_cpu_data.x86_vendor &
+ (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
+ mask = (((uint64_t)p->feat.max_subleaf << 32) |
+ ((uint32_t)mask | p->feat._7b0));
d->arch.pv.cpuidmasks->_7ab0 = mask;
}
--
2.11.0
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https://lists.xenproject.org/mailman/listinfo/xen-develOn Mon, Sep 09, 2019 at 04:51:24PM +0100, Andrew Cooper wrote:
> 7a0 is an integer field, not a mask - taking the logical and of the hardware
> and policy values results in nonsense. Instead, take the policy value
> directly.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wl@xen.org>
> CC: Roger Pau Monné <roger.pau@citrix.com>
>
> Even Rome hardware has 7[0].eax still as 0, and there is no sensible reason to
> set max_subleaf higher at this point, so this is only a latent bug for now.
> ---
> xen/arch/x86/domctl.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
> index 1e98fc8009..35ad8cb51c 100644
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
> {
> uint64_t mask = cpuidmask_defaults._7ab0;
> - uint32_t eax = ctl->eax;
> - uint32_t ebx = p->feat._7b0;
>
> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> - mask &= ((uint64_t)eax << 32) | ebx;
> + /*
> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
> + * wholesale from the policy, but clamp the features in 7[0].ebx
> + * per usual.
> + */
> + if ( boot_cpu_data.x86_vendor &
> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
> + ((uint32_t)mask | p->feat._7b0));
Why do you set the high bits of the mask (63:30) with the max subleaf?
According to the document I have bits 63:30 are reserved, and that
seems to match the expected CPUID return value, that lists CPUID
Fn0000_0007_EAX_x0 content as reserved.
Thanks, Roger.
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On 10/09/2019 10:29, Roger Pau Monné wrote:
> On Mon, Sep 09, 2019 at 04:51:24PM +0100, Andrew Cooper wrote:
>> 7a0 is an integer field, not a mask - taking the logical and of the hardware
>> and policy values results in nonsense. Instead, take the policy value
>> directly.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> ---
>> CC: Jan Beulich <JBeulich@suse.com>
>> CC: Wei Liu <wl@xen.org>
>> CC: Roger Pau Monné <roger.pau@citrix.com>
>>
>> Even Rome hardware has 7[0].eax still as 0, and there is no sensible reason to
>> set max_subleaf higher at this point, so this is only a latent bug for now.
>> ---
>> xen/arch/x86/domctl.c | 13 +++++++++----
>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
>> index 1e98fc8009..35ad8cb51c 100644
>> --- a/xen/arch/x86/domctl.c
>> +++ b/xen/arch/x86/domctl.c
>> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
>> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
>> {
>> uint64_t mask = cpuidmask_defaults._7ab0;
>> - uint32_t eax = ctl->eax;
>> - uint32_t ebx = p->feat._7b0;
>>
>> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>> - mask &= ((uint64_t)eax << 32) | ebx;
>> + /*
>> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
>> + * wholesale from the policy, but clamp the features in 7[0].ebx
>> + * per usual.
>> + */
>> + if ( boot_cpu_data.x86_vendor &
>> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
>> + ((uint32_t)mask | p->feat._7b0));
> Why do you set the high bits of the mask (63:30) with the max subleaf?
63:32
> According to the document I have bits 63:30 are reserved, and that
> seems to match the expected CPUID return value, that lists CPUID
> Fn0000_0007_EAX_x0 content as reserved.
Yes, but reserved doesn't mean "will #GP". As I said on IRC, this MSR
*is* the value which gets forwarded into a CPUID invocation, and setting
max_subleaf to 0xdead does work fine.
The point here is that in the future, on hardware capable of
max_subleaf=2 and being levelled to max_subleaf=1, the value observed in
CPUID should be 1, not 0.
The latter is what the current logic does, and is broken. The CPUID
derivation logic will ensure that policy max_subleaf <= hardware
max_subleaf.
~Andrew
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On Tue, Sep 10, 2019 at 10:35:26AM +0100, Andrew Cooper wrote:
> On 10/09/2019 10:29, Roger Pau Monné wrote:
> > On Mon, Sep 09, 2019 at 04:51:24PM +0100, Andrew Cooper wrote:
> >> 7a0 is an integer field, not a mask - taking the logical and of the hardware
> >> and policy values results in nonsense. Instead, take the policy value
> >> directly.
> >>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> >> ---
> >> CC: Jan Beulich <JBeulich@suse.com>
> >> CC: Wei Liu <wl@xen.org>
> >> CC: Roger Pau Monné <roger.pau@citrix.com>
> >>
> >> Even Rome hardware has 7[0].eax still as 0, and there is no sensible reason to
> >> set max_subleaf higher at this point, so this is only a latent bug for now.
> >> ---
> >> xen/arch/x86/domctl.c | 13 +++++++++----
> >> 1 file changed, 9 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
> >> index 1e98fc8009..35ad8cb51c 100644
> >> --- a/xen/arch/x86/domctl.c
> >> +++ b/xen/arch/x86/domctl.c
> >> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
> >> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
> >> {
> >> uint64_t mask = cpuidmask_defaults._7ab0;
> >> - uint32_t eax = ctl->eax;
> >> - uint32_t ebx = p->feat._7b0;
> >>
> >> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> >> - mask &= ((uint64_t)eax << 32) | ebx;
> >> + /*
> >> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
> >> + * wholesale from the policy, but clamp the features in 7[0].ebx
> >> + * per usual.
> >> + */
> >> + if ( boot_cpu_data.x86_vendor &
> >> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> >> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
> >> + ((uint32_t)mask | p->feat._7b0));
> > Why do you set the high bits of the mask (63:30) with the max subleaf?
>
> 63:32
>
> > According to the document I have bits 63:30 are reserved, and that
> > seems to match the expected CPUID return value, that lists CPUID
> > Fn0000_0007_EAX_x0 content as reserved.
>
> Yes, but reserved doesn't mean "will #GP". As I said on IRC, this MSR
> *is* the value which gets forwarded into a CPUID invocation, and setting
> max_subleaf to 0xdead does work fine.
>
> The point here is that in the future, on hardware capable of
> max_subleaf=2 and being levelled to max_subleaf=1, the value observed in
> CPUID should be 1, not 0.
Oh, and that's from Intel specification which does indeed list
Fn0000_0007_EAX_x0 as returning the max sub-leaf, and the expectation
is that AMD will follow suit.
> The latter is what the current logic does, and is broken. The CPUID
> derivation logic will ensure that policy max_subleaf <= hardware
> max_subleaf.
Reviewed-by: Roger Pau Monné <roger.pau@cirtrix.com>
Thanks, Roger.
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On 10/09/2019 10:57, Roger Pau Monné wrote:
> On Tue, Sep 10, 2019 at 10:35:26AM +0100, Andrew Cooper wrote:
>> On 10/09/2019 10:29, Roger Pau Monné wrote:
>>> On Mon, Sep 09, 2019 at 04:51:24PM +0100, Andrew Cooper wrote:
>>>> 7a0 is an integer field, not a mask - taking the logical and of the hardware
>>>> and policy values results in nonsense. Instead, take the policy value
>>>> directly.
>>>>
>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>>> ---
>>>> CC: Jan Beulich <JBeulich@suse.com>
>>>> CC: Wei Liu <wl@xen.org>
>>>> CC: Roger Pau Monné <roger.pau@citrix.com>
>>>>
>>>> Even Rome hardware has 7[0].eax still as 0, and there is no sensible reason to
>>>> set max_subleaf higher at this point, so this is only a latent bug for now.
>>>> ---
>>>> xen/arch/x86/domctl.c | 13 +++++++++----
>>>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
>>>> index 1e98fc8009..35ad8cb51c 100644
>>>> --- a/xen/arch/x86/domctl.c
>>>> +++ b/xen/arch/x86/domctl.c
>>>> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
>>>> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
>>>> {
>>>> uint64_t mask = cpuidmask_defaults._7ab0;
>>>> - uint32_t eax = ctl->eax;
>>>> - uint32_t ebx = p->feat._7b0;
>>>>
>>>> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>>>> - mask &= ((uint64_t)eax << 32) | ebx;
>>>> + /*
>>>> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
>>>> + * wholesale from the policy, but clamp the features in 7[0].ebx
>>>> + * per usual.
>>>> + */
>>>> + if ( boot_cpu_data.x86_vendor &
>>>> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>>>> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
>>>> + ((uint32_t)mask | p->feat._7b0));
>>> Why do you set the high bits of the mask (63:30) with the max subleaf?
>> 63:32
>>
>>> According to the document I have bits 63:30 are reserved, and that
>>> seems to match the expected CPUID return value, that lists CPUID
>>> Fn0000_0007_EAX_x0 content as reserved.
>> Yes, but reserved doesn't mean "will #GP". As I said on IRC, this MSR
>> *is* the value which gets forwarded into a CPUID invocation, and setting
>> max_subleaf to 0xdead does work fine.
>>
>> The point here is that in the future, on hardware capable of
>> max_subleaf=2 and being levelled to max_subleaf=1, the value observed in
>> CPUID should be 1, not 0.
> Oh, and that's from Intel specification which does indeed list
> Fn0000_0007_EAX_x0 as returning the max sub-leaf, and the expectation
> is that AMD will follow suit.
The AMD CPUID documentation does identify CPUID 7[0].eax as
max_subleaf. It just isn't cross referenced very well with the MSR.
>
>> The latter is what the current logic does, and is broken. The CPUID
>> derivation logic will ensure that policy max_subleaf <= hardware
>> max_subleaf.
> Reviewed-by: Roger Pau Monné <roger.pau@cirtrix.com>
Thanks,
~Andrew
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On 09.09.2019 17:51, Andrew Cooper wrote:
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
> {
> uint64_t mask = cpuidmask_defaults._7ab0;
> - uint32_t eax = ctl->eax;
> - uint32_t ebx = p->feat._7b0;
>
> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> - mask &= ((uint64_t)eax << 32) | ebx;
> + /*
> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
> + * wholesale from the policy, but clamp the features in 7[0].ebx
> + * per usual.
> + */
> + if ( boot_cpu_data.x86_vendor &
> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
> + ((uint32_t)mask | p->feat._7b0));
Assuming you mean & instead of | here, with it fixed
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Otherwise I'm afraid I don't understand, and need further
explanation.
Jan
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On 10/09/2019 11:24, Jan Beulich wrote:
> On 09.09.2019 17:51, Andrew Cooper wrote:
>> --- a/xen/arch/x86/domctl.c
>> +++ b/xen/arch/x86/domctl.c
>> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
>> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
>> {
>> uint64_t mask = cpuidmask_defaults._7ab0;
>> - uint32_t eax = ctl->eax;
>> - uint32_t ebx = p->feat._7b0;
>>
>> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>> - mask &= ((uint64_t)eax << 32) | ebx;
>> + /*
>> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
>> + * wholesale from the policy, but clamp the features in 7[0].ebx
>> + * per usual.
>> + */
>> + if ( boot_cpu_data.x86_vendor &
>> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
>> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
>> + ((uint32_t)mask | p->feat._7b0));
> Assuming you mean & instead of | here, with it fixed
Oops - I do.
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
Thanks,
~Andrew
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