Re: [PATCH v6 06/21] arm64: Move VHE-specific SPE setup to mutate_to_vhe()

[Marc Zyngier]

Hi Will,

On 2021-02-03 21:13, Will Deacon wrote:
> 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@xxxxxxxxxx>
> > Acked-by: David Brazdil <dbrazdil@xxxxxxxxxx>
> > Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > ---
> >  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.

That's definitely a brain fart, and is what we need on the nVHE path,
not here. Doing the same thing twice isn't exactly helpful.

> 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).

I don't think it does. We only clear the E2PB bits (harmless, as you 
point
out above), and OR something that is either 0 (no SPE) or MDCR_EL2_TPMS.
In any case, the HPMN bits are preserved (having been set during the 
nVHE
setup).

I think the following patch addresses the above issue, which I'll squash
with the original patch. Please shout if I missed anything.

Thanks,

        M.

diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index aa7e8d592295..3e08dcc924b5 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -115,29 +115,9 @@ 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
-	mov	x2, #MDCR_EL2_TPMS
-
-skip_spe:
-	// For VHE, use EL2 translation and disable access from EL1
+	// Use EL2 translations for SPE 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

 	// Transfer the MM state from EL1 to EL2

--
Jazz is not dead. It just smells funny...