Re: [PATCH v5 08/12] KVM: arm64: re-factor hyp.S debug register code

[Christoffer Dall]

On Fri, May 29, 2015 at 10:30:24AM +0100, Alex Bennée wrote:
> This is a pre-cursor to sharing the code with the guest debug support.
> This replaces the big macro that fishes data out of a fixed location
> with a more general helper macro to restore a set of debug registers. It
> uses macro substitution so it can be re-used for debug control and value
> registers. It does however rely on the debug registers being 64 bit
> aligned (as they happen to be in the hyp ABI).
> 
> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
> 
> ---
> v3:
>   - return to the patch series
>   - add save and restore targets
>   - change register use and document
> v4:
>   - keep original setup/restore names
>   - don't use split u32/u64 structure yet
> ---
>  arch/arm64/kvm/hyp.S | 519 ++++++++++++++-------------------------------------
>  1 file changed, 140 insertions(+), 379 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index 74e63d8..9c4897d 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S


[...]

> @@ -465,195 +318,52 @@
>  	msr	mdscr_el1,	x25
>  .endm
>  
> -.macro restore_debug
> -	// x2: base address for cpu context
> -	// x3: tmp register
> -
> -	mrs	x26, id_aa64dfr0_el1
> -	ubfx	x24, x26, #12, #4	// Extract BRPs
> -	ubfx	x25, x26, #20, #4	// Extract WRPs
> -	mov	w26, #15
> -	sub	w24, w26, w24		// How many BPs to skip
> -	sub	w25, w26, w25		// How many WPs to skip
> -
> -	add	x3, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
> +.macro restore_debug type
> +        // x4: pointer to register set
> +        // x5: number of registers to skip

nit: use tabs instead of spaces here...

> +	// x6..x22 trashed
>  

[...]

> @@ -887,12 +597,63 @@ __restore_sysregs:
>  	restore_sysregs
>  	ret
>  
> +/* Save debug state */
>  __save_debug:
> -	save_debug
> +	// x0: base address for vcpu context
> +	// x2: ptr to current CPU context
> +	// x4/x5: trashed

I had a bunch of questions here which I think you missed last time
around:
 1. why do we need the vcpu context?
 2. what does 'current' mean here?
 3. you're also trashing everything that save_debug trashes, so x4/5,
    x6-x22 trashed would be more correct

> +
> +	mrs	x26, id_aa64dfr0_el1
> +	ubfx	x24, x26, #12, #4	// Extract BRPs
> +	ubfx	x25, x26, #20, #4	// Extract WRPs
> +	mov	w26, #15
> +	sub	w24, w26, w24		// How many BPs to skip
> +	sub	w25, w26, w25		// How many WPs to skip
> +
> +	mov     x5, x24
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
> +	save_debug dbgbcr
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGBVR0_EL1)
> +	save_debug dbgbvr
> +
> +	mov     x5, x25
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGWCR0_EL1)
> +	save_debug dbgwcr
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGWVR0_EL1)
> +	save_debug dbgwvr
> +
> +	mrs	x21, mdccint_el1
> +	str	x21, [x2, #CPU_SYSREG_OFFSET(MDCCINT_EL1)]
>  	ret
>  
> +/* Restore debug state */
>  __restore_debug:
> -	restore_debug
> +	// x0: base address for cpu context
> +	// x2: ptr to current CPU context
> +	// x4/x5: trashed

and you missed these comments too, basically same stuff, but why was it
'cpu' here and not 'vcpu' like above?

note again, that you're explicitly touching x24, xx25, and x26 here as
well, so shouldn't they be listed as trashed?

> +
> +	mrs	x26, id_aa64dfr0_el1
> +	ubfx	x24, x26, #12, #4	// Extract BRPs
> +	ubfx	x25, x26, #20, #4	// Extract WRPs
> +	mov	w26, #15
> +	sub	w24, w26, w24		// How many BPs to skip
> +	sub	w25, w26, w25		// How many WPs to skip
> +
> +	mov     x5, x24
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGBCR0_EL1)
> +	restore_debug dbgbcr
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGBVR0_EL1)
> +	restore_debug dbgbvr
> +
> +	mov     x5, x25
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGWCR0_EL1)
> +	restore_debug dbgwcr
> +	add	x4, x2, #CPU_SYSREG_OFFSET(DBGWVR0_EL1)
> +	restore_debug dbgwvr
> +
> +	ldr	x21, [x2, #CPU_SYSREG_OFFSET(MDCCINT_EL1)]
> +	msr	mdccint_el1, x21
> +
>  	ret
>  
>  __save_fpsimd:

Thanks,
-Christoffer
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