Re: [PATCH v5 5/7] arm64: head: Init PMSCR_EL2.{PA,PCT} when entered at EL2 without VHE

From: Mark Rutland
Date: Mon Oct 02 2017 - 06:04:37 EST


On Thu, Sep 28, 2017 at 03:09:49PM +0100, Will Deacon wrote:
> When booting at EL2, ensure that we permit the EL1 host to sample
> physical addresses and physical counter values using SPE.
>
> Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> ---
> arch/arm64/kernel/head.S | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 7434ec0c7a27..c370e270ae55 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -479,14 +479,21 @@ set_hcr:
>
> /* Statistical profiling */
> ubfx x0, x1, #32, #4 // Check ID_AA64DFR0_EL1 PMSVer
> - cbz x0, 6f // Skip if SPE not present
> - cbnz x2, 5f // VHE?
> + cbz x0, 7f // Skip if SPE not present
> + cbnz x2, 6f // VHE?
> + mrs_s x4, SYS_PMBIDR_EL1 // If SPE available at EL2,
> + and x4, x4, #(1 << SYS_PMBIDR_EL1_P_SHIFT)
> + cbnz x4, 5f // then permit sampling of physical
> + mov x4, #(1 << SYS_PMSCR_EL2_PCT_SHIFT | \
> + 1 << SYS_PMSCR_EL2_PA_SHIFT)
> + msr_s SYS_PMSCR_EL2, x4 // addresses and physical counter

As a general note, I find these right-hand-side comments difficult to
read, especially here with multiple line gaps mid-sentence.

If I'm alone in that view, there's no reason to change them, but
otherwise it might make sense to replace the more complex comments with
/* */ comment blocks on their own lines...

The logic looks fine to me, so FWIW:

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> +5:
> mov x1, #(MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT)
> orr x3, x3, x1 // If we don't have VHE, then
> - b 6f // use EL1&0 translation.
> -5: // For VHE, use EL2 translation
> + b 7f // use EL1&0 translation.
> +6: // For VHE, use EL2 translation
> orr x3, x3, #MDCR_EL2_TPMS // and disable access from EL1
> -6:
> +7:
> msr mdcr_el2, x3 // Configure debug traps
>
> /* Stage-2 translation */
> --
> 2.1.4
>