linux-kernel - Re: [QUERY] lguest64

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Message-ID: <51FFD9D8.3000704@zytor.com>
Date:	Mon, 05 Aug 2013 09:59:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Gleb Natapov <gleb@...hat.com>,
	Mukesh Rathor <mukesh.rathor@...cle.com>,
	Mike Rapoport <mike.rapoport@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	xen-devel@...ts.xensource.com
Subject: Re: [QUERY] lguest64

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?

	-hpa


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