linux-kernel - Re: [PATCH v6 06/21] arm64: Move VHE-specific SPE setup to mutate_to

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Date:   Wed, 3 Feb 2021 21:13:19 +0000
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jing Zhang <jingzhangos@...gle.com>,
        Ajay Patil <pajay@....qualcomm.com>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        Srinivas Ramana <sramana@...eaurora.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v6 06/21] arm64: Move VHE-specific SPE setup to
 mutate_to_vhe()

Hi Marc,

On Mon, Feb 01, 2021 at 11:56:22AM +0000, Marc Zyngier wrote:
> There isn't much that a VHE kernel needs on top of whatever has
> been done for nVHE, so let's move the little we need to the
> VHE stub (the SPE setup), and drop the init_el2_state macro.
> 
> No expected functional change.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Acked-by: David Brazdil <dbrazdil@...gle.com>
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> ---
>  arch/arm64/kernel/hyp-stub.S | 28 +++++++++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index 373ed2213e1d..6b5c73cf9d52 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -92,9 +92,6 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
>  	msr	hcr_el2, x0
>  	isb
>  
> -	// Doesn't do much on VHE, but still, worth a shot
> -	init_el2_state vhe
> -
>  	// Use the EL1 allocated stack, per-cpu offset
>  	mrs	x0, sp_el1
>  	mov	sp, x0
> @@ -107,6 +104,31 @@ SYM_CODE_START_LOCAL(mutate_to_vhe)
>  	mrs_s	x0, SYS_VBAR_EL12
>  	msr	vbar_el1, x0
>  
> +	// Fixup SPE configuration, if supported...
> +	mrs	x1, id_aa64dfr0_el1
> +	ubfx	x1, x1, #ID_AA64DFR0_PMSVER_SHIFT, #4
> +	mov	x2, xzr
> +	cbz	x1, skip_spe
> +
> +	// ... and not owned by EL3
> +	mrs_s	x0, SYS_PMBIDR_EL1
> +	and	x0, x0, #(1 << SYS_PMBIDR_EL1_P_SHIFT)
> +	cbnz	x0, skip_spe
> +
> +	// Let the SPE driver in control of the sampling
> +	mrs_s	x0, SYS_PMSCR_EL1
> +	bic	x0, x0, #(1 << SYS_PMSCR_EL2_PCT_SHIFT)
> +	bic	x0, x0, #(1 << SYS_PMSCR_EL2_PA_SHIFT)
> +	msr_s	SYS_PMSCR_EL1, x0

Why do we need to touch pmscr_el1 at all? The SPE driver should take care of
that, no? If you drop the pmscr_el1 accesses, I think you can drop the
pmbidr_el1 check as well. And actually, then why even check dfr0? Doing the
bic for the mdcr_el1.e2pb bits is harmless.

> +	mov	x2, #MDCR_EL2_TPMS
> +
> +skip_spe:
> +	// For VHE, use EL2 translation and disable access from EL1
> +	mrs	x0, mdcr_el2
> +	bic	x0, x0, #(MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT)
> +	orr	x0, x0, x2
> +	msr	mdcr_el2, x0

Doesn't this undo the setting of mdcr_el2.hpmn if SPE is not present or
unavailable? (This wouldn't be an issue if we removed the skip_spe paths
altogether).

Will