Re: [QUERY] lguest64

From: H. Peter Anvin
Date: Mon Aug 05 2013 - 12:59:37 EST

On 08/05/2013 09:50 AM, Konrad Rzeszutek Wilk wrote:
>>> Let me iterate down what the experimental patch uses:
>>> struct pv_init_ops pv_init_ops;
>>> [still use xen_patch, but I think that is not needed anymore]
>>> struct pv_time_ops pv_time_ops;
>>> [we need that as we are using the PV clock source]
>>> struct pv_cpu_ops pv_cpu_ops;
>>> [only end up using cpuid. This one is a tricky one. We could
>>> arguable remove it but it does do some filtering - for example
>>> THERM is turned off, or MWAIT if a certain hypercall tells us to
>>> disable that. Since this is now a trapped operation this could be
>>> handled in the hypervisor - but then it would be in charge of
>>> filtering certain CPUID - and this is at bootup - so there is not
>>> user interaction. This needs a bit more of thinking]
>> read_msr/write_msr in this one make all msr accesses safe. IIRC there
>> are MSRs that Linux uses without checking cpuid bits.
>> IA32_PERF_CAPABILITIES for instance is used without checking PDCM bit.
> Right, those are needed as well. Completly forgot about them.

CPUID is not too bad. RDMSR/WRMSR is actually worse since there are
some MSRs which are performance-critical. The really messy pvops are
the memory-related ones, as they don't match the hardware behavior.

Similarly, beyond pvops, what new assumptions does this code add to the
code base?


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