[PATCH] arm64: Do not trap PMSNEVFR_EL1

[Alexandru Elisei]

Commit 31c00d2aeaa2 ("arm64: Disable fine grained traps on boot") zeroed
the fine grained trap registers to prevent unwanted register traps from
occuring. However, for the PMSNEVFR_EL1 register, the corresponding
HDFGRTR_EL2.nPMSNEVFR_EL1 field must be 1 to disable trapping. Set the
field to 1 if FEAT_SPEv1p2 is detected.

Fixes: 31c00d2aeaa2 ("arm64: Disable fine grained traps on boot")
Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
---
Based on v5.14-rc7. Also, we could write 1 << 62 to HDFGRTR_EL2 unconditionally
since the field is RAZ/WI if !FEAT_SPEv1p2. I don't have a strong preference for
either approaches, but I chose this implementation because it's clearer (even
though it's more verbose and it's one extra trap on NV).

Tested on the model, using boot-wrapper built from commit 5cd6238ec4ef
("aarch32: fix .globl replacement"). Without this patch, in NVHE mode, the model
freezes when I try to read PMSNEVFR_EL1. With this patch, the model doesn't hang
when I read the register, but it hangs when I write to it. I've gone throught
the pseudocode for reading and writing to PMSNEVFR_EL1 and from what I can tell
nothing should be trapping the accesses. On top of that, this is what I tried on
the model with this patch applied:

1. VHE mode, I can read and write to PMSNEVFR_EL1 without any issues, so the
hang is not caused by an incorrect EL3 configuration.

2. NVHE mode, I can read and write just fine to *PMSEVFR_EL1*, so the hang is
not caused by an EL2 trap that affects the rest of the profiling control
registers. I have tried printing the HDFGRTR_EL2 value in this situation using
semihosting, the value is what it is programmed by __init_el2_fgt (that is,
1 << 62).

At this point, I am inclined to think it's a model bug because reading works,
but writing causes a hang and that looks very suspicious to me. I'm going to
open a model bug internally and see what comes of it.

 arch/arm64/include/asm/el2_setup.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/el2_setup.h b/arch/arm64/include/asm/el2_setup.h
index b83fb24954b7..8a9adb2039fd 100644
--- a/arch/arm64/include/asm/el2_setup.h
+++ b/arch/arm64/include/asm/el2_setup.h
@@ -149,7 +149,16 @@
 	ubfx	x1, x1, #ID_AA64MMFR0_FGT_SHIFT, #4
 	cbz	x1, .Lskip_fgt_\@
 
-	msr_s	SYS_HDFGRTR_EL2, xzr
+	mov	x0, xzr
+	mrs	x1, id_aa64dfr0_el1
+	ubfx	x1, x1, #ID_AA64DFR0_PMSVER_SHIFT, #4
+	cmp	x1, #3
+	b.lt	.Lset_fgt_\@
+	/* Set HDFGRTR_EL2.nPMSNEVFR_EL1 to disable the register trap */
+	orr	x0, x0, #(1 << 62)
+
+.Lset_fgt_\@:
+	msr_s	SYS_HDFGRTR_EL2, x0
 	msr_s	SYS_HDFGWTR_EL2, xzr
 	msr_s	SYS_HFGRTR_EL2, xzr
 	msr_s	SYS_HFGWTR_EL2, xzr
-- 
2.33.0