Re: [PATCH v14 27/39] arm64/sme: Provide Kconfig for SME

Hi Mark,

On 19.04.2022 13:22, Mark Brown wrote:

Now that basline support for the Scalable Matrix Extension (SME) is present introduce the Kconfig option allowing it to be built. While the feature registers don't impose a strong requirement for a system with SME to support SVE at runtime the support for streaming mode SVE is mostly shared with normal SVE so depend on SVE.

Signed-off-by: Mark Brown broonie@kernel.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com

This patchset landed in linux next-20220426. By default SME is enabled and it breaks CPU hot-plug on all my arm64 test systems. Bisect points this patch, because it finally enables this feature. Here is a report from QEMU's arm64 virt machine:

# for i in /sys/devices/system/cpu/cpu[1-9]; do echo 0 >$i/online; done psci: CPU1 killed (polled 0 ms) # cat /proc/cpuinfo | grep processor | wc -l 1 # for i in /sys/devices/system/cpu/cpu[1-9]; do echo 1 >$i/online; done ------------[ cut here ]------------ kernel BUG at arch/arm64/kernel/cpufeature.c:1353! Internal error: Oops - BUG: 0 [#1] PREEMPT SMP Modules linked in: bluetooth ecdh_generic ecc rfkill ipv6 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.18.0-rc3+ #4891 Hardware name: linux,dummy-virt (DT) pstate: 200001c5 (nzCv dAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : __read_sysreg_by_encoding+0x350/0x354 lr : has_cpuid_feature+0x6c/0xe0 ... Call trace:  __read_sysreg_by_encoding+0x350/0x354  has_cpuid_feature+0x6c/0xe0  verify_local_cpu_caps+0x98/0x130  check_local_cpu_capabilities+0x2c/0x270  secondary_start_kernel+0xc0/0x170  __secondary_switched+0xa0/0xa4 Code: d53802d3 17ffff49 d5380233 17ffff47 (d4210000) ---[ end trace 0000000000000000 ]--- Kernel panic - not syncing: Attempted to kill the idle task! SMP: stopping secondary CPUs Kernel Offset: 0x4e81fb600000 from 0xffff800008000000 PHYS_OFFSET: 0xffff98f240000000 CPU features: 0x440,00033c08,00001086 Memory Limit: none ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

Disabling SME on top of next-20220426 hides this issue.

---

arch/arm64/Kconfig | 11 +++++++++++ 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 57c4c995965f..0897984918e8 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1939,6 +1939,17 @@ config ARM64_SVE booting the kernel. If unsure and you are not observing these symptoms, you should assume that it is safe to say Y. +config ARM64_SME

• bool "ARM Scalable Matrix Extension support"
• default y
• depends on ARM64_SVE
• help

•  The Scalable Matrix Extension (SME) is an extension to the AArch64
  

•  execution state which utilises a substantial subset of the SVE
  

•  instruction set, together with the addition of new architectural
  

•  register state capable of holding two dimensional matrix tiles to
  

•  enable various matrix operations.
  

• config ARM64_MODULE_PLTS bool "Use PLTs to allow module memory to spill over into vmalloc area" depends on MODULES

Best regards