Re: [Xen-devel] [PATCH 4/4] x86/vmx: Drop vmx_msr_state infrastructure

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.02.17 at 15:32, <andrew.cooper3@xxxxxxxxxx> wrote:
> To avoid leaking host MSR state into guests, guest LSTAR, STAR and
> SYSCALL_MASK state is unconditionally loaded when switching into guest
> context.
> 
> Attempting to dirty-track the state is pointless; host state is always
> restoring upon exit from guest context, meaning that guest state is always
> considered dirty.
> 
> Drop struct vmx_msr_state, enum VMX_INDEX_MSR_* and msr_index[].  The guests
> MSR values are stored plainly in arch_vmx_struct, in the same way as shadow_gs
> and cstar are.  vmx_restore_guest_msrs() and long_mode_do_msr_write() ensure
> that the hardware MSR values are always up-to-date.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

However, the description above made me think whether always
saving/restoring these MSRs is really needed (and desirable):
We don't need the host values in place unless we context switch
to a PV guest, so perhaps we should rather write them in
paravirt_ctxt_switch_to()?

Jan


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