[PATCH v2] xen: fix cpuid reporting on PVH Dom0

[PATCH v2] xen: fix cpuid reporting on PVH Dom0

[Roger Pau Monne]

dab11417d also caused some problems regarding HVM guest creation on
PVH Dom0, mainly the CR4 mask returned by hvm_cr4_guest_reserved_bits
changed from 0xfffffffffffff800 to 0xfffffffffffff893, which means HVM
guests created from a PVH Dom0 are unable to set VME, PVI, PSE or PGE
CR4 flags.

This is because cpuid on PVH guests mask PSE, PGE, PSE36 and VME
flags, so the white listing done in xc_cpuid_hvm_policy doesn't enable
those features, and the guest ends up with a very restrictive cpuid
policy.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---
Changes since RFC:
 - Expose the cpuid flags to all PVH guests and not only
   hardware/control domains.
---
 xen/arch/x86/traps.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 677074b..465b196 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -803,12 +803,16 @@ void pv_cpuid(struct cpu_user_regs *regs)
     if ( (regs->eax & 0x7fffffff) == 0x00000001 )
     {
         /* Modify Feature Information. */
-        __clear_bit(X86_FEATURE_VME, &d);
         if ( !cpu_has_apic )
             __clear_bit(X86_FEATURE_APIC, &d);
-        __clear_bit(X86_FEATURE_PSE, &d);
-        __clear_bit(X86_FEATURE_PGE, &d);
-        __clear_bit(X86_FEATURE_PSE36, &d);
+        if ( !is_pvh_vcpu(curr) )
+        {
+            __clear_bit(X86_FEATURE_PSE, &d);
+            __clear_bit(X86_FEATURE_PGE, &d);
+            __clear_bit(X86_FEATURE_PSE36, &d);
+            __clear_bit(X86_FEATURE_VME, &d);
+        }
+
     }
 
     switch ( (uint32_t)regs->eax )
-- 
1.7.7.5 (Apple Git-26)


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Re: [PATCH v2] xen: fix cpuid reporting on PVH Dom0

[Andrew Cooper]

On 01/08/14 16:26, Roger Pau Monne wrote:
> dab11417d also caused some problems regarding HVM guest creation on
> PVH Dom0, mainly the CR4 mask returned by hvm_cr4_guest_reserved_bits
> changed from 0xfffffffffffff800 to 0xfffffffffffff893, which means HVM
> guests created from a PVH Dom0 are unable to set VME, PVI, PSE or PGE
> CR4 flags.
>
> This is because cpuid on PVH guests mask PSE, PGE, PSE36 and VME
> flags, so the white listing done in xc_cpuid_hvm_policy doesn't enable
> those features, and the guest ends up with a very restrictive cpuid
> policy.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> Cc: Jan Beulich <JBeulich@suse.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> Changes since RFC:
>  - Expose the cpuid flags to all PVH guests and not only
>    hardware/control domains.
> ---
>  xen/arch/x86/traps.c |   12 ++++++++----
>  1 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
> index 677074b..465b196 100644
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -803,12 +803,16 @@ void pv_cpuid(struct cpu_user_regs *regs)
>      if ( (regs->eax & 0x7fffffff) == 0x00000001 )
>      {
>          /* Modify Feature Information. */
> -        __clear_bit(X86_FEATURE_VME, &d);
>          if ( !cpu_has_apic )
>              __clear_bit(X86_FEATURE_APIC, &d);
> -        __clear_bit(X86_FEATURE_PSE, &d);
> -        __clear_bit(X86_FEATURE_PGE, &d);
> -        __clear_bit(X86_FEATURE_PSE36, &d);

Newline here...

> +        if ( !is_pvh_vcpu(curr) )
> +        {
> +            __clear_bit(X86_FEATURE_PSE, &d);
> +            __clear_bit(X86_FEATURE_PGE, &d);
> +            __clear_bit(X86_FEATURE_PSE36, &d);
> +            __clear_bit(X86_FEATURE_VME, &d);

Why do PVH guests care about VME?  They can't use it as far as I am aware.

> +        }
> +

... and not here.

>      }
>  
>      switch ( (uint32_t)regs->eax )


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Re: [PATCH v2] xen: fix cpuid reporting on PVH Dom0

[Jan Beulich]

>>> On 04.08.14 at 12:32, <andrew.cooper3@citrix.com> wrote:
> On 01/08/14 16:26, Roger Pau Monne wrote:
>> --- a/xen/arch/x86/traps.c
>> +++ b/xen/arch/x86/traps.c
>> @@ -803,12 +803,16 @@ void pv_cpuid(struct cpu_user_regs *regs)
>>      if ( (regs->eax & 0x7fffffff) == 0x00000001 )
>>      {
>>          /* Modify Feature Information. */
>> -        __clear_bit(X86_FEATURE_VME, &d);
>>          if ( !cpu_has_apic )
>>              __clear_bit(X86_FEATURE_APIC, &d);
>> -        __clear_bit(X86_FEATURE_PSE, &d);
>> -        __clear_bit(X86_FEATURE_PGE, &d);
>> -        __clear_bit(X86_FEATURE_PSE36, &d);
> 
> Newline here...
> 
>> +        if ( !is_pvh_vcpu(curr) )
>> +        {
>> +            __clear_bit(X86_FEATURE_PSE, &d);
>> +            __clear_bit(X86_FEATURE_PGE, &d);
>> +            __clear_bit(X86_FEATURE_PSE36, &d);
>> +            __clear_bit(X86_FEATURE_VME, &d);
> 
> Why do PVH guests care about VME?  They can't use it as far as I am aware.

I don't think it particularly cares, but it also seems unnecessary and
inconsistent to hide a feature from it without need.

>> +        }
>> +
> 
> ... and not here.

I've already taken care of these formatting issues in the to-be-
committed version.

Jan