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SubjectRe: [PATCH v6 06/21] arm64: Move VHE-specific SPE setup to mutate_to_vhe()
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@kernel.org>
>> Acked-by: David Brazdil <dbrazdil@google.com>
>> Acked-by: Catalin Marinas <catalin.marinas@arm.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.

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...

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