linux-kernel - Re: [PATCH V3 6/7] arm64/boot: Enable EL2 requirements for FEAT

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Message-ID: <96bae61a-c9a0-4b9a-af4f-b6fc6202bccd@arm.com>
Date: Wed, 18 Dec 2024 10:55:43 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Rob Herring <robh@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>,
 Suzuki K Poulose <suzuki.poulose@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Brown <broonie@...nel.org>, Mark Rutland <mark.rutland@....com>,
 kvmarm@...ts.linux.dev, linux-doc@...r.kernel.org
Subject: Re: [PATCH V3 6/7] arm64/boot: Enable EL2 requirements for
 FEAT_Debugv8p9

[....]

On 12/17/24 23:23, Rob Herring wrote:
>> Something like the commit
>>
>> commit 31c00d2aeaa2da89361f5b64a64ca831433be5fc
>> Author: Mark Brown <broonie@...nel.org>
>> Date:   Thu Apr 1 19:09:40 2021 +0100
>>
>>     arm64: Disable fine grained traps on boot
>>
>>     The arm64 FEAT_FGT extension introduces a set of traps to EL2 for accesses
>>     to small sets of registers and instructions from EL1 and EL0.  Currently
>>     Linux makes no use of this feature, ensure that it is not active at boot by
>>     disabling the traps during EL2 setup.
>>
>>
>>>
>>> I just realized I forgot to add FGT2 setup for the PMUv3.9 features I
>>> already added in 6.12 and 6.13. So this really needs to land sooner
>>> rather than later to add that.
>> Not sure if I got this correctly. Are you suggesting to carve out __init_el2_fgt2()
>> from the series and post separately with PMUv3.9 requirements and fallback clearing
>> for all FEAT_FGT2 trap config registers as mentioned above ?
> Yes, as it needs to not be held up by any of the debug issues Mark
> raised. Also, it may need to be back ported to 6.12. And for that we'd
> want the PMU parts, but not the Debug. I still have to figure out what
> needs to be done on the KVM side.

Hi Rob,

I did go through all the five FEAT_FGT2 trap control registers and it
seems like the following are the controls available for FEAT_PMUv3p9
based registers. Although PMZR_EL0 does not get used in kernel right
now but still might be a good idea to include anyway. Please let me
know, if I might have missed something else related to FEAT_PMUv3p9.

HDFGRTR2_EL2_nPMUACR_EL1	(mrs PMUACR_EL1)
HDFGWTR2_EL2_nPMUACR_EL1	(msr PMUACR_EL1)
HDFGWTR2_EL2_nPMZR_EL0		(msr PMZR_EL0)

Following will be the change required for __init_el2_fgt2() along with
all the tools sysreg updates required for the mentioned registers here.

--- a/arch/arm64/include/asm/el2_setup.h
+++ b/arch/arm64/include/asm/el2_setup.h
@@ -233,6 +233,31 @@
 .Lskip_fgt_\@:
 .endm
 
+.macro __init_el2_fgt2
+       mrs     x1, id_aa64mmfr0_el1
+       ubfx    x1, x1, #ID_AA64MMFR0_EL1_FGT_SHIFT, #4
+       cmp     x1, #ID_AA64MMFR0_EL1_FGT_FGT2
+       b.lt    .Lskip_fgt2_\@
+
+       mov     x0, xzr
+       mov     x2, xzr
+       mrs     x1, id_aa64dfr0_el1
+       ubfx    x1, x1, #ID_AA64DFR0_EL1_PMUVer_SHIFT, #4
+       cmp     x1, #ID_AA64DFR0_EL1_PMUVer_V3P9
+       b.lt    .Lskip_pmuv3p9_\@
+
+       orr     x0, x0, #HDFGRTR2_EL2_nPMUACR_EL1
+       orr     x2, x2, #HDFGWTR2_EL2_nPMUACR_EL1
+       orr     x2, x2, #HDFGWTR2_EL2_nPMZR_EL0
+.Lskip_pmuv3p9_\@:
+       msr_s   SYS_HDFGRTR2_EL2, x0
+       msr_s   SYS_HDFGWTR2_EL2, x2
+       msr_s   SYS_HFGRTR2_EL2, xzr
+       msr_s   SYS_HFGWTR2_EL2, xzr
+       msr_s   SYS_HFGITR2_EL2, xzr
+.Lskip_fgt2_\@:
+.endm
+
 .macro __init_el2_gcs
        mrs_s   x1, SYS_ID_AA64PFR1_EL1
        ubfx    x1, x1, #ID_AA64PFR1_EL1_GCS_SHIFT, #4
@@ -283,6 +308,7 @@
        __init_el2_nvhe_idregs
        __init_el2_cptr
        __init_el2_fgt
+       __init_el2_fgt2
         __init_el2_gcs
 .endm