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Re: [Qemu-devel] [PATCH] resent: x86/cpuid: propagate further CPUID leaf
Re: [Qemu-devel] [PATCH] resent: x86/cpuid: propagate further CPUID leafs when -cpu host
Tue, 25 May 2010 15:21:46 +0200
Thunderbird 126.96.36.199 (X11/20090820)
Anthony Liguori wrote:
I think that should be fixed. Although -cpu host is not a wise choice
for migration, even without these additional leaves the feature bits
probably don't match between source and target.
On 05/21/2010 02:50 AM, Andre Przywara wrote:
-cpu host currently only propagates the CPU's family/model/stepping,
the brand name and the feature bits.
Add a whitelist of safe CPUID leafs to let the guest see the actual
CPU's cache details and other things.
Signed-off-by: Andre Przywara<address@hidden>
The problem I can see is that this greatly increases the chances of
problems with live migration since we don't migrate the cpuid state.
What's the benefit of exposing this information to the guest?
That is mostly to propagate the cache size and organization parameters
to the guest:
>> +/* safe CPUID leafs to propagate to guest if -cpu host is specified
>> + * Intel defined leafs:
>> + * Cache descriptors (0x02)
>> + * Deterministic cache parameters (0x04)
>> + * Monitor/MWAIT parameters (0x05)
>> + *
>> + * AMD defined leafs:
>> + * L1 Cache and TLB (0x05)
>> + * L2+L3 TLB (0x06)
>> + * LongMode address size (0x08)
>> + * 1GB page TLB (0x19)
>> + * Performance optimization (0x1A)
>> + */
Since at least L1 and L2 caches are mostly private to vCPUs, I see no
reason to disguise them.
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