[Xen-devel] [PATCH RFC] xen: fix cpuid reporting on PVH Dom0

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

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 Monnà <roger.pau@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
TBH, I'm not sure what's the best way to fix this, the cpuid stuff is
so convoluted and it's done in so many different places that I've
probably missed something.
---
 xen/arch/x86/traps.c |   13 +++++++++----
 1 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 677074b..0a46f75 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -803,12 +803,17 @@ 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) || !is_control_domain(curr->domain) ||
+             !is_hardware_domain(curr->domain) )
+        {
+            __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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