Re: [Xen-devel] [PATCH v2 4/5] x86/hvm: Handle x2apic MSRs via the new guest_{rd, wr}msr() infrastructure

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

On Wed, Mar 07, 2018 at 06:58:35PM +0000, Andrew Cooper wrote:
> Dispatch from the guest_{rd,wr}msr() functions.  The read side should be safe
> outside of current context, but the write side is definitely not.  As the
> toolstack has no legitimate reason to access the APIC registers via this
> interface (not least because whether they are accessible at all depends on
> guest settings), unilaterally reject access attempts outside of current
> context.
> 
> Rename to guest_{rd,wr}msr_x2apic() for consistency, and alter the functions
> to use X86EMUL_EXCEPTION rather than X86EMUL_UNHANDLEABLE.  The previous
> callers turned UNHANDLEABLE into EXCEPTION, but using UNHANDLEABLE will now
> interfere with the fallback to legacy MSR handling.
> 
> While altering guest_rdmsr_x2apic() make a couple of minor improvements.
> Reformat the initialiser for readable[] so it indents in a more natural way,
> and alter high to be a 64bit integer to avoid shifting 0 by 32 in the common
> path.
> 
> Observant people might notice that we now don't let PV guests read the x2apic
> MSRs.  They should never have been able to in the first place.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Roger.

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