[PATCH 02/26] KVM: PPC: Book3S PR: add new parameter (guest MSR) for kvmppc_save_tm()/kvmppc_restore_tm()

[Paul Mackerras]

On Thu, Jan 11, 2018 at 06:11:15PM +0800, wei.guo.simon at gmail.com wrote:
> From: Simon Guo <wei.guo.simon at gmail.com>
> 
> HV KVM and PR KVM need different MSR source to indicate whether
> treclaim. or trecheckpoint. is necessary.
> 
> This patch add new parameter (guest MSR) for these kvmppc_save_tm/
> kvmppc_restore_tm() APIs:
> - For HV KVM, it is VCPU_MSR
> - For PR KVM, it is current host MSR or VCPU_SHADOW_SRR1
> 
> This enhancement enables these 2 APIs to be reused by PR KVM later.
> And the patch keeps HV KVM logic unchanged.
> 
> This patch also reworks kvmppc_save_tm()/kvmppc_restore_tm() to
> have a clean ABI: r3 for vcpu and r4 for guest_msr.
> 
> Signed-off-by: Simon Guo <wei.guo.simon at gmail.com>

Question: why do you switch from using HSTATE_HOST_R1 to HSTATE_SCRATCH2

> @@ -42,11 +45,11 @@ _GLOBAL(kvmppc_save_tm)
>  	rldimi	r8, r0, MSR_TM_LG, 63-MSR_TM_LG
>  	mtmsrd	r8
>  
> -	ld	r5, VCPU_MSR(r9)
> -	rldicl. r5, r5, 64 - MSR_TS_S_LG, 62
> +	rldicl. r4, r4, 64 - MSR_TS_S_LG, 62
>  	beq	1f	/* TM not active in guest. */
>  
> -	std	r1, HSTATE_HOST_R1(r13)
> +	std	r1, HSTATE_SCRATCH2(r13)

... here?

> @@ -166,17 +173,17 @@ _GLOBAL(kvmppc_restore_tm)
>  	 * The user may change these outside of a transaction, so they must
>  	 * always be context switched.
>  	 */
> -	ld	r5, VCPU_TFHAR(r4)
> -	ld	r6, VCPU_TFIAR(r4)
> -	ld	r7, VCPU_TEXASR(r4)
> +	ld	r5, VCPU_TFHAR(r3)
> +	ld	r6, VCPU_TFIAR(r3)
> +	ld	r7, VCPU_TEXASR(r3)
>  	mtspr	SPRN_TFHAR, r5
>  	mtspr	SPRN_TFIAR, r6
>  	mtspr	SPRN_TEXASR, r7
>  
> -	ld	r5, VCPU_MSR(r4)
> +	mr	r5, r4
>  	rldicl. r5, r5, 64 - MSR_TS_S_LG, 62
>  	beqlr		/* TM not active in guest */
> -	std	r1, HSTATE_HOST_R1(r13)
> +	std	r1, HSTATE_SCRATCH2(r13)

and here?

Please add a paragraph to the patch description explaining why you are
making that change.

Paul.