Subject: Re: [PATCH 07/13] KVM: PPC: Book3S HV: Adjust host/guest context switch for POWER9

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Fri, 18 Nov 2016 20:05:47 +0530

Paul Mackerras <[email-masked]> writes:

> Some special-purpose registers that were present and accessible
> by guests on POWER8 no longer exist on POWER9, so this adds
> feature sections to ensure that we don't try to context-switch
> them when going into or out of a guest on POWER9.  These are
> all relatively obscure, rarely-used registers, but we had to
> context-switch them on POWER8 to avoid creating a covert channel.
> They are: SPMC1, SPMC2, MMCRS, CSIGR, TACR, TCSCR, and ACOP.

We don't need to context-switch them even when running a power8 compat
guest ?

>
> Signed-off-by: Paul Mackerras <[email-masked]>
> ---
>  arch/powerpc/kvm/book3s_hv_rmhandlers.S | 50 ++++++++++++++++++++-------------
>  1 file changed, 30 insertions(+), 20 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index dc25467..d422014 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -752,14 +752,16 @@ END_FTR_SECTION_IFSET(CPU_FTR_PMAO_BUG)
>  BEGIN_FTR_SECTION
>  	ld	r5, VCPU_MMCR + 24(r4)
>  	ld	r6, VCPU_SIER(r4)
> +	mtspr	SPRN_MMCR2, r5
> +	mtspr	SPRN_SIER, r6
> +BEGIN_FTR_SECTION_NESTED(96)
>  	lwz	r7, VCPU_PMC + 24(r4)
>  	lwz	r8, VCPU_PMC + 28(r4)
>  	ld	r9, VCPU_MMCR + 32(r4)
> -	mtspr	SPRN_MMCR2, r5
> -	mtspr	SPRN_SIER, r6
>  	mtspr	SPRN_SPMC1, r7
>  	mtspr	SPRN_SPMC2, r8
>  	mtspr	SPRN_MMCRS, r9
> +END_FTR_SECTION_NESTED(CPU_FTR_ARCH_300, 0, 96)
>  END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>  	mtspr	SPRN_MMCR0, r3
>  	isync
> @@ -815,20 +817,22 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
>  	mtspr	SPRN_EBBHR, r8
>  	ld	r5, VCPU_EBBRR(r4)
>  	ld	r6, VCPU_BESCR(r4)
> -	ld	r7, VCPU_CSIGR(r4)
> -	ld	r8, VCPU_TACR(r4)
> +	lwz	r7, VCPU_GUEST_PID(r4)
> +	ld	r8, VCPU_WORT(r4)
>  	mtspr	SPRN_EBBRR, r5
>  	mtspr	SPRN_BESCR, r6
> -	mtspr	SPRN_CSIGR, r7
> -	mtspr	SPRN_TACR, r8
> +	mtspr	SPRN_PID, r7
> +	mtspr	SPRN_WORT, r8
> +BEGIN_FTR_SECTION
>  	ld	r5, VCPU_TCSCR(r4)
>  	ld	r6, VCPU_ACOP(r4)
> -	lwz	r7, VCPU_GUEST_PID(r4)
> -	ld	r8, VCPU_WORT(r4)
> +	ld	r7, VCPU_CSIGR(r4)
> +	ld	r8, VCPU_TACR(r4)
>  	mtspr	SPRN_TCSCR, r5
>  	mtspr	SPRN_ACOP, r6
> -	mtspr	SPRN_PID, r7
> -	mtspr	SPRN_WORT, r8
> +	mtspr	SPRN_CSIGR, r7
> +	mtspr	SPRN_TACR, r8
> +END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
>  8:
>  
>  	/*
> @@ -1343,20 +1347,22 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
>  	std	r8, VCPU_EBBHR(r9)
>  	mfspr	r5, SPRN_EBBRR
>  	mfspr	r6, SPRN_BESCR
> -	mfspr	r7, SPRN_CSIGR
> -	mfspr	r8, SPRN_TACR
> +	mfspr	r7, SPRN_PID
> +	mfspr	r8, SPRN_WORT
>  	std	r5, VCPU_EBBRR(r9)
>  	std	r6, VCPU_BESCR(r9)
> -	std	r7, VCPU_CSIGR(r9)
> -	std	r8, VCPU_TACR(r9)
> +	stw	r7, VCPU_GUEST_PID(r9)
> +	std	r8, VCPU_WORT(r9)
> +BEGIN_FTR_SECTION
>  	mfspr	r5, SPRN_TCSCR
>  	mfspr	r6, SPRN_ACOP
> -	mfspr	r7, SPRN_PID
> -	mfspr	r8, SPRN_WORT
> +	mfspr	r7, SPRN_CSIGR
> +	mfspr	r8, SPRN_TACR
>  	std	r5, VCPU_TCSCR(r9)
>  	std	r6, VCPU_ACOP(r9)
> -	stw	r7, VCPU_GUEST_PID(r9)
> -	std	r8, VCPU_WORT(r9)
> +	std	r7, VCPU_CSIGR(r9)
> +	std	r8, VCPU_TACR(r9)
> +END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
>  	/*
>  	 * Restore various registers to 0, where non-zero values
>  	 * set by the guest could disrupt the host.
> @@ -1365,12 +1371,14 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
>  	mtspr	SPRN_IAMR, r0
>  	mtspr	SPRN_CIABR, r0
>  	mtspr	SPRN_DAWRX, r0
> -	mtspr	SPRN_TCSCR, r0
>  	mtspr	SPRN_WORT, r0
> +BEGIN_FTR_SECTION
> +	mtspr	SPRN_TCSCR, r0
>  	/* Set MMCRS to 1<<31 to freeze and disable the SPMC counters */
>  	li	r0, 1
>  	sldi	r0, r0, 31
>  	mtspr	SPRN_MMCRS, r0
> +END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300)
>  8:
>  
>  	/* Save and reset AMR and UAMOR before turning on the MMU */
> @@ -1504,15 +1512,17 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>  	stw	r8, VCPU_PMC + 20(r9)
>  BEGIN_FTR_SECTION
>  	mfspr	r5, SPRN_SIER
> +	std	r5, VCPU_SIER(r9)
> +BEGIN_FTR_SECTION_NESTED(96)
>  	mfspr	r6, SPRN_SPMC1
>  	mfspr	r7, SPRN_SPMC2
>  	mfspr	r8, SPRN_MMCRS
> -	std	r5, VCPU_SIER(r9)
>  	stw	r6, VCPU_PMC + 24(r9)
>  	stw	r7, VCPU_PMC + 28(r9)
>  	std	r8, VCPU_MMCR + 32(r9)
>  	lis	r4, 0x8000
>  	mtspr	SPRN_MMCRS, r4
> +END_FTR_SECTION_NESTED(CPU_FTR_ARCH_300, 0, 96)
>  END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
>  22:
>  	/* Clear out SLB */
> -- 
> 2.7.4
>
> --
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