From: Alexandru Elisei <alexandru.elisei@arm.com>
To: maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, broonie@kernel.org,
Catalin Marinas <Catalin.Marinas@arm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH] arm64: Do not trap PMSNEVFR_EL1
Date: Tue, 24 Aug 2021 14:28:45 +0100 [thread overview]
Message-ID: <01117fe3-d4fa-a735-36e1-ac9003e7b5cb@arm.com> (raw)
In-Reply-To: <20210824132459.562923-1-alexandru.elisei@arm.com>
Errr... somehow I forgot to add the arm64 maintainers. Fixing that.
On 8/24/21 2:24 PM, Alexandru Elisei wrote:
> 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@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
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WARNING: multiple messages have this Message-ID (diff)
From: Alexandru Elisei <alexandru.elisei@arm.com>
To: maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, broonie@kernel.org,
Catalin Marinas <Catalin.Marinas@arm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH] arm64: Do not trap PMSNEVFR_EL1
Date: Tue, 24 Aug 2021 14:28:45 +0100 [thread overview]
Message-ID: <01117fe3-d4fa-a735-36e1-ac9003e7b5cb@arm.com> (raw)
In-Reply-To: <20210824132459.562923-1-alexandru.elisei@arm.com>
Errr... somehow I forgot to add the arm64 maintainers. Fixing that.
On 8/24/21 2:24 PM, Alexandru Elisei wrote:
> 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@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
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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-08-24 13:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 13:24 [PATCH] arm64: Do not trap PMSNEVFR_EL1 Alexandru Elisei
2021-08-24 13:24 ` Alexandru Elisei
2021-08-24 13:28 ` Alexandru Elisei [this message]
2021-08-24 13:28 ` Alexandru Elisei
2021-08-24 15:10 ` Mark Brown
2021-08-24 15:10 ` Mark Brown
2021-08-24 15:30 ` Alexandru Elisei
2021-08-24 15:30 ` Alexandru Elisei
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