Re: [PATCH 2/2] arm64: cpufeatures: Only check for NV1 if NV is present

[Marc Zyngier <maz@kernel.org>]

On Tue, 13 Feb 2024 11:14:37 +0000,
Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> 
> Hi
> 
> On 12.02.2024 15:47, Marc Zyngier wrote:
> > We handle ID_AA64MMFR4_EL1.E2H0 being 0 as NV1 being present.
> > However, this is only true if FEAT_NV is implemented.
> >
> > Add the required check to has_nv1(), avoiding spuriously advertising
> > NV1 on HW that doesn't have NV at all.
> >
> > Fixes: da9af5071b25 ("arm64: cpufeature: Detect HCR_EL2.NV1 being RES0")
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> 
> This patch in turn introduces the following warning during boot 
> (observed on today's linux-next):
> 
> CPU: All CPU(s) started at EL2
> CPU features: detected: 32-bit EL0 Support
> CPU features: detected: 32-bit EL1 Support
> CPU features: detected: CRC32 instructions
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at arch/arm64/kernel/cpufeature.c:3369 
> this_cpu_has_cap+0x18/0x70
> Modules linked in:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.8.0-rc4-next-20240213 #8014
> Hardware name: Khadas VIM3 (DT)
> pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : this_cpu_has_cap+0x18/0x70
> lr : has_nv1+0x24/0xcc
> ...
> Call trace:
>   this_cpu_has_cap+0x18/0x70
>   update_cpu_capabilities+0x50/0x134
>   setup_system_features+0x30/0x120
>   smp_cpus_done+0x48/0xb4
>   smp_init+0x7c/0x8c
>   kernel_init_freeable+0x18c/0x4e4
>   kernel_init+0x20/0x1d8
>   ret_from_fork+0x10/0x20
> irq event stamp: 2846
> hardirqs last  enabled at (2845): [<ffff80008012cf5c>] 
> console_unlock+0x164/0x190
> hardirqs last disabled at (2846): [<ffff80008123a078>] el1_dbg+0x24/0x8c
> softirqs last  enabled at (2842): [<ffff800080010a60>] 
> __do_softirq+0x4a0/0x4e8
> softirqs last disabled at (2827): [<ffff8000800169b0>] 
> ____do_softirq+0x10/0x1c
> ---[ end trace 0000000000000000 ]---
> alternatives: applying system-wide alternatives

This is nothing short of embarrassing. It looks like I somehow managed
to drop CONFIG_PREEMPT from my test config, making it impossible to
identify these issues. Apologies for that.

The following patch fixes it for me. Could you please give it a go?

Thanks,

	M.

From cd75279d3b6c387c13972b61c486a203d9652e97 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@kernel.org>
Date: Tue, 13 Feb 2024 13:37:57 +0000
Subject: [PATCH] arm64: cpufeatures: Fix FEAT_NV check when checking for
 FEAT_NV1

Using this_cpu_has_cap() has the potential to go wrong when
used system-wide on a preemptible kernel. Instead, use the
__system_matches_cap() helper when checking for FEAT_NV in the
FEAT_NV1 probing helper.

Fixes: 3673d01a2f55 ("arm64: cpufeatures: Only check for NV1 if NV is present")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 3421b684d340..f309fd542c20 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1812,7 +1812,7 @@ static bool has_nv1(const struct arm64_cpu_capabilities *entry, int scope)
 		{}
 	};
 
-	return (this_cpu_has_cap(ARM64_HAS_NESTED_VIRT) &&
+	return (__system_matches_cap(ARM64_HAS_NESTED_VIRT) &&
 		!(has_cpuid_feature(entry, scope) ||
 		  is_midr_in_range_list(read_cpuid_id(), nv1_ni_list)));
 }
-- 
2.39.2


-- 
Without deviation from the norm, progress is not possible.