Re: [Xen-devel] [PATCH 06/11] x86: Reorganise and rename debug register fields in struct vcpu

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

On Mon, Jun 04, 2018 at 02:59:10PM +0100, Andrew Cooper wrote:
> Reusing debugreg[5] for the PV emulated IO breakpoint information is confusing
> to read.  Instead, introduce a dr7_emul field in pv_vcpu for the pupose.
> 
> With the PV emulation out of the way, debugreg[4,5] are entirely unused and
> don't need to be stored.
> 
> Rename debugreg[0..3] to dr[0..3] to reduce code volume, but keep them as an
> array because their behaviour is identical and this helps simplfy some of the
> PV handling.  Introduce dr6 and dr7 fields to replace debugreg[6,7] which
> removes the storage for debugreg[4,5].
> 
> Two minor alterations on the PV side is that merging of the emulated state
> happens along with the other dr handling, rather than much later, and
> arch_set_info_guest() now checks the return value from set_debugreg() fails
> the hypercall rather than silently discarding the values.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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

> diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
> index 197f8d6..59d5e4a 100644
> --- a/xen/include/asm-x86/domain.h
> +++ b/xen/include/asm-x86/domain.h
> @@ -500,6 +500,12 @@ struct pv_vcpu
>      unsigned long shadow_ldt_mapcnt;
>      spinlock_t shadow_ldt_lock;
>  
> +    /*
> +     * %dr7 bits the guest has set, but aren't loaded into hardware, and are
> +     * completely emulated.
> +     */
> +    uint32_t dr7_emul;

Upper 32bit are reserved ATM, but won't it be better to just use a
unsigned long (like it's used below to store the registers)?

Roger.

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