| Message ID | 20241021181434.1052974-1-maz@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | arm64: Add command-line override for ID_AA64MMFR0_EL1.ECV | expand |
On Mon, 21 Oct 2024 19:14:34 +0100, Marc Zyngier wrote: > It appears that relatively popular hardware out there implements > the CNTPOFF_EL2 variant of FEAT_ECV, advertises it via ID_AA64MMFR0_EL1, > but cannot be bothered to set SCR_EL3.ECVEn to 1. > > You would probably think that "this is fine, EL3 will take the > trap on access to CNTPOFF_EL2 and flip the ECVEn bit", as that's > what a semi-decent firmware implementation would do. > > [...] Applied to arm64 (for-next/misc), thanks! [1/1] arm64: Add command-line override for ID_AA64MMFR0_EL1.ECV https://git.kernel.org/arm64/c/358dd4a9bdac
diff --git a/arch/arm64/kernel/pi/idreg-override.c b/arch/arm64/kernel/pi/idreg-override.c index 29d4b6244a6f6..fbc37b2733e20 100644 --- a/arch/arm64/kernel/pi/idreg-override.c +++ b/arch/arm64/kernel/pi/idreg-override.c @@ -38,6 +38,15 @@ struct ftr_set_desc { #define FIELD(n, s, f) { .name = n, .shift = s, .width = 4, .filter = f } +static const struct ftr_set_desc mmfr0 __prel64_initconst = { + .name = "id_aa64mmfr0", + .override = &id_aa64mmfr0_override, + .fields = { + FIELD("ecv", ID_AA64MMFR0_EL1_ECV_SHIFT, NULL), + {} + }, +}; + static bool __init mmfr1_vh_filter(u64 val) { /* @@ -196,6 +205,7 @@ static const struct ftr_set_desc sw_features __prel64_initconst = { static const PREL64(const struct ftr_set_desc, reg) regs[] __prel64_initconst = { + { &mmfr0 }, { &mmfr1 }, { &mmfr2 }, { &pfr0 },
It appears that relatively popular hardware out there implements the CNTPOFF_EL2 variant of FEAT_ECV, advertises it via ID_AA64MMFR0_EL1, but cannot be bothered to set SCR_EL3.ECVEn to 1. You would probably think that "this is fine, EL3 will take the trap on access to CNTPOFF_EL2 and flip the ECVEn bit", as that's what a semi-decent firmware implementation would do. But no. None of that. This particular implementation takes the trap, considers its purpose in life, decides that it has none, and *RESETS* the system. Yes, x1e001de, I'm talking about you. In order to allow this machine to be promoted slightly above the level of a glorified door-stop, add a new "id_aa64mmfr0.ecv" override. allowing the kernel to pretend this option was never there. Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/kernel/pi/idreg-override.c | 10 ++++++++++ 1 file changed, 10 insertions(+)