* [PATCH] arm64: Restore forced disabling of KPTI on ThunderX
@ 2021-09-22 13:59 dann frazier
2021-09-22 14:11 ` Mark Brown
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: dann frazier @ 2021-09-22 13:59 UTC (permalink / raw)
To: Catalin Marinas, Will Deacon
Cc: Suzuki K Poulose, Mark Brown, linux-arm-kernel, Marc Zyngier,
Mark Rutland
A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h")
is that cpucaps are now sorted, changing the enumeration order. This
assumed no dependencies between cpucaps, which turned out not to be true
in one case. UNMAP_KERNEL_AT_EL0 currently needs to be processed after
WORKAROUND_CAVIUM_27456. ThunderX systems are incompatible with KPTI, so
unmap_kernel_at_el0() bails if WORKAROUND_CAVIUM_27456 is set. But because
of the sorting, WORKAROUND_CAVIUM_27456 will not yet have been considered
when unmap_kernel_at_el0() checks for it, so the kernel tries to
run w/ KPTI - and quickly falls over.
Because all ThunderX implementations have homogeneous CPUs, we can remove
this dependency by just checking the current CPU for the erratum.
Fixes: 0c6c2d3615ef ("arm64: Generate cpucaps.h")
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: dann frazier <dann.frazier@canonical.com>
---
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 f8a3067d10c6..7275b49034f3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1528,7 +1528,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
* ThunderX leads to apparent I-cache corruption of kernel text, which
* ends as well as you might imagine. Don't even try.
*/
- if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
+ if (this_cpu_has_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
str = "ARM64_WORKAROUND_CAVIUM_27456";
__kpti_forced = -1;
}
--
2.33.0
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^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Restore forced disabling of KPTI on ThunderX
2021-09-22 13:59 [PATCH] arm64: Restore forced disabling of KPTI on ThunderX dann frazier
@ 2021-09-22 14:11 ` Mark Brown
2021-09-22 18:59 ` Marc Zyngier
2021-09-23 9:41 ` Suzuki K Poulose
2 siblings, 0 replies; 5+ messages in thread
From: Mark Brown @ 2021-09-22 14:11 UTC (permalink / raw)
To: dann frazier
Cc: Catalin Marinas, Will Deacon, Suzuki K Poulose, linux-arm-kernel,
Marc Zyngier, Mark Rutland
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On Wed, Sep 22, 2021 at 07:59:24AM -0600, dann frazier wrote:
> A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> is that cpucaps are now sorted, changing the enumeration order. This
> assumed no dependencies between cpucaps, which turned out not to be true
Reviwed-by: Mark Brown <broonie@kernel.org>
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Restore forced disabling of KPTI on ThunderX
2021-09-22 13:59 [PATCH] arm64: Restore forced disabling of KPTI on ThunderX dann frazier
2021-09-22 14:11 ` Mark Brown
@ 2021-09-22 18:59 ` Marc Zyngier
2021-09-23 9:41 ` Suzuki K Poulose
2 siblings, 0 replies; 5+ messages in thread
From: Marc Zyngier @ 2021-09-22 18:59 UTC (permalink / raw)
To: dann frazier
Cc: Catalin Marinas, Will Deacon, Suzuki K Poulose, Mark Brown,
linux-arm-kernel, Mark Rutland
On Wed, 22 Sep 2021 14:59:24 +0100,
dann frazier <dann.frazier@canonical.com> wrote:
>
> A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> is that cpucaps are now sorted, changing the enumeration order. This
> assumed no dependencies between cpucaps, which turned out not to be true
> in one case. UNMAP_KERNEL_AT_EL0 currently needs to be processed after
> WORKAROUND_CAVIUM_27456. ThunderX systems are incompatible with KPTI, so
> unmap_kernel_at_el0() bails if WORKAROUND_CAVIUM_27456 is set. But because
> of the sorting, WORKAROUND_CAVIUM_27456 will not yet have been considered
> when unmap_kernel_at_el0() checks for it, so the kernel tries to
> run w/ KPTI - and quickly falls over.
>
> Because all ThunderX implementations have homogeneous CPUs, we can remove
> this dependency by just checking the current CPU for the erratum.
>
> Fixes: 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: stable@vger.kernel.org # 5.13+
> Signed-off-by: dann frazier <dann.frazier@canonical.com>
> ---
> 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 f8a3067d10c6..7275b49034f3 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1528,7 +1528,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> * ThunderX leads to apparent I-cache corruption of kernel text, which
> * ends as well as you might imagine. Don't even try.
> */
> - if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
> + if (this_cpu_has_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
> str = "ARM64_WORKAROUND_CAVIUM_27456";
> __kpti_forced = -1;
> }
Ouch, nice catch. Hopefully, nobody will build a big-little system
using TX1 in this instance of the universe.
Acked-by: Marc Zyngier <maz@kernel.org>
M.
--
Without deviation from the norm, progress is not possible.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Restore forced disabling of KPTI on ThunderX
2021-09-22 13:59 [PATCH] arm64: Restore forced disabling of KPTI on ThunderX dann frazier
2021-09-22 14:11 ` Mark Brown
2021-09-22 18:59 ` Marc Zyngier
@ 2021-09-23 9:41 ` Suzuki K Poulose
2021-09-23 14:45 ` dann frazier
2 siblings, 1 reply; 5+ messages in thread
From: Suzuki K Poulose @ 2021-09-23 9:41 UTC (permalink / raw)
To: dann frazier, Catalin Marinas, Will Deacon
Cc: Mark Brown, linux-arm-kernel, Marc Zyngier, Mark Rutland
On 22/09/2021 14:59, dann frazier wrote:
> A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> is that cpucaps are now sorted, changing the enumeration order. This
> assumed no dependencies between cpucaps, which turned out not to be true
> in one case. UNMAP_KERNEL_AT_EL0 currently needs to be processed after
> WORKAROUND_CAVIUM_27456. ThunderX systems are incompatible with KPTI, so
> unmap_kernel_at_el0() bails if WORKAROUND_CAVIUM_27456 is set. But because
> of the sorting, WORKAROUND_CAVIUM_27456 will not yet have been considered
> when unmap_kernel_at_el0() checks for it, so the kernel tries to
> run w/ KPTI - and quickly falls over.
>
> Because all ThunderX implementations have homogeneous CPUs, we can remove
> this dependency by just checking the current CPU for the erratum.
>
> Fixes: 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: stable@vger.kernel.org # 5.13+
> Signed-off-by: dann frazier <dann.frazier@canonical.com>
> ---
> 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 f8a3067d10c6..7275b49034f3 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1528,7 +1528,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> * ThunderX leads to apparent I-cache corruption of kernel text, which
> * ends as well as you might imagine. Don't even try.
> */
> - if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
> + if (this_cpu_has_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
Please could you also update the comment right above this line to
explain, why we do this and why this is fine (just like you have
in the description) ? Something like :
* Since we cannot rely on the order of the cpucaps
* we cannot rely on the cpus_have_*cap() helpers to
* detect the erratum on the system. However, since
* affected CPUs are always in a homoegeneous configuration
* we could rely on this_cpu_has_cap()
*/
So that looking at the code, it is easier to comprehend what we
figured out in the mailing list (and the description)
With that:
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Suzuki
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Restore forced disabling of KPTI on ThunderX
2021-09-23 9:41 ` Suzuki K Poulose
@ 2021-09-23 14:45 ` dann frazier
0 siblings, 0 replies; 5+ messages in thread
From: dann frazier @ 2021-09-23 14:45 UTC (permalink / raw)
To: Suzuki K Poulose
Cc: Catalin Marinas, Will Deacon, Mark Brown, linux-arm-kernel,
Marc Zyngier, Mark Rutland
On Thu, Sep 23, 2021 at 10:41:00AM +0100, Suzuki K Poulose wrote:
> On 22/09/2021 14:59, dann frazier wrote:
> > A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> > is that cpucaps are now sorted, changing the enumeration order. This
> > assumed no dependencies between cpucaps, which turned out not to be true
> > in one case. UNMAP_KERNEL_AT_EL0 currently needs to be processed after
> > WORKAROUND_CAVIUM_27456. ThunderX systems are incompatible with KPTI, so
> > unmap_kernel_at_el0() bails if WORKAROUND_CAVIUM_27456 is set. But because
> > of the sorting, WORKAROUND_CAVIUM_27456 will not yet have been considered
> > when unmap_kernel_at_el0() checks for it, so the kernel tries to
> > run w/ KPTI - and quickly falls over.
> >
> > Because all ThunderX implementations have homogeneous CPUs, we can remove
> > this dependency by just checking the current CPU for the erratum.
> >
> > Fixes: 0c6c2d3615ef ("arm64: Generate cpucaps.h")
> > Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Cc: stable@vger.kernel.org # 5.13+
> > Signed-off-by: dann frazier <dann.frazier@canonical.com>
> > ---
> > 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 f8a3067d10c6..7275b49034f3 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -1528,7 +1528,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> > * ThunderX leads to apparent I-cache corruption of kernel text, which
> > * ends as well as you might imagine. Don't even try.
> > */
> > - if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
> > + if (this_cpu_has_cap(ARM64_WORKAROUND_CAVIUM_27456)) {
>
> Please could you also update the comment right above this line to
> explain, why we do this and why this is fine (just like you have
> in the description) ? Something like :
>
> * Since we cannot rely on the order of the cpucaps
> * we cannot rely on the cpus_have_*cap() helpers to
> * detect the erratum on the system. However, since
> * affected CPUs are always in a homoegeneous configuration
> * we could rely on this_cpu_has_cap()
> */
>
> So that looking at the code, it is easier to comprehend what we
> figured out in the mailing list (and the description)
Sure thing, v2 coming shortly.
-dann
> With that:
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>
> Suzuki
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^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-09-23 14:48 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-22 13:59 [PATCH] arm64: Restore forced disabling of KPTI on ThunderX dann frazier
2021-09-22 14:11 ` Mark Brown
2021-09-22 18:59 ` Marc Zyngier
2021-09-23 9:41 ` Suzuki K Poulose
2021-09-23 14:45 ` dann frazier
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