[PATCH v2 1/2] powerpc/powernv: Get L1D flush requirements from device-tree

Tue Apr 5 17:20:54 AEST 2022

On Tue, 5 Apr 2022 at 06:13, Michael Ellerman <mpe at ellerman.id.au> wrote:
>
> Joel Stanley <joel at jms.id.au> writes:
> > On Mon, 4 Apr 2022 at 10:15, Russell Currey <ruscur at russell.cc> wrote:
> >>
> >> The device-tree properties no-need-l1d-flush-msr-pr-1-to-0 and
> >> no-need-l1d-flush-kernel-on-user-access are the equivalents of
> >> H_CPU_BEHAV_NO_L1D_FLUSH_ENTRY and H_CPU_BEHAV_NO_L1D_FLUSH_UACCESS
> >> from the H_GET_CPU_CHARACTERISTICS hcall on pseries respectively.
> >>
> >> In commit d02fa40d759f ("powerpc/powernv: Remove POWER9 PVR version
> >> check for entry and uaccess flushes") the condition for disabling the
> >> L1D flush on kernel entry and user access was changed from any non-P9
> >> CPU to only checking P7 and P8.  Without the appropriate device-tree
> >> checks for newer processors on powernv, these flushes are unnecessarily
> >> enabled on those systems.  This patch corrects this.
> >>
> >> Fixes: d02fa40d759f ("powerpc/powernv: Remove POWER9 PVR version check for entry and uaccess flushes")
> >> Reported-by: Joel Stanley <joel at jms.id.au>
> >> Signed-off-by: Russell Currey <ruscur at russell.cc>
> >
> > I booted both patches in this series on a power10 powernv machine,
> > applied on top of v5.18-rc1:
> >
> > $ dmesg |grep -i flush
> > [    0.000000] rfi-flush: fallback displacement flush available
> > [    0.000000] rfi-flush: patched 12 locations (no flush)
> > [    0.000000] count-cache-flush: flush disabled.
> > [    0.000000] link-stack-flush: flush disabled.
> >
> > $ grep . /sys/devices/system/cpu/vulnerabilities/*
> > /sys/devices/system/cpu/vulnerabilities/itlb_multihit:Not affected
> > /sys/devices/system/cpu/vulnerabilities/l1tf:Not affected
> > /sys/devices/system/cpu/vulnerabilities/mds:Not affected
> > /sys/devices/system/cpu/vulnerabilities/meltdown:Not affected
> > /sys/devices/system/cpu/vulnerabilities/spec_store_bypass:Not affected
> > /sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: __user
> > pointer sanitization, ori31 speculation barrier enabled
> > /sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation:
> > Software count cache flush (hardware accelerated), Software link stack
> > flush
> > /sys/devices/system/cpu/vulnerabilities/srbds:Not affected
> > /sys/devices/system/cpu/vulnerabilities/tsx_async_abort:Not affected
> >
> > Does that match what we expect?
>
> AFAIK yes. Happy for ruscur to correct me though.
>
> Can you also try running the kernel selftests under
> tools/testing/selftests/powerpc/security/ ?

Here's the results when booted with no_spectrev2 (which I keep on
doing by accident, as this machine has it in it's nvram):

make[1]: Entering directory
'/home/joel/dev/kernels/linus/tools/testing/selftests/powerpc/security'
TAP version 13
1..5
# selftests: powerpc/security: rfi_flush
# test: rfi_flush_test
# tags: git_version:v5.18-rc1-0-g312310928417
# PASS (L1D misses with rfi_flush=0: 63101900 < 95000000) [10/10 pass]
# PASS (L1D misses with rfi_flush=1: 196001003 > 190000000) [10/10 pass]
# success: rfi_flush_test
ok 1 selftests: powerpc/security: rfi_flush
# selftests: powerpc/security: entry_flush
# test: entry_flush_test
# tags: git_version:v5.18-rc1-0-g312310928417
# PASS (L1D misses with entry_flush=0: 52766044 < 95000000) [10/10 pass]
# PASS (L1D misses with entry_flush=1: 196082833 > 190000000) [10/10 pass]
# success: entry_flush_test
ok 2 selftests: powerpc/security: entry_flush
# selftests: powerpc/security: uaccess_flush
# test: uaccess_flush_test
# tags: git_version:v5.18-rc1-0-g312310928417
# PASS (L1D misses with uaccess_flush=0: 68646267 < 95000000) [10/10 pass]
# PASS (L1D misses with uaccess_flush=1: 194177355 > 190000000) [10/10 pass]
# success: uaccess_flush_test
ok 3 selftests: powerpc/security: uaccess_flush
# selftests: powerpc/security: spectre_v2
# test: spectre_v2
# tags: git_version:v5.18-rc1-0-g312310928417
# sysfs reports: 'Vulnerable'
#  PM_BR_PRED_CCACHE: result          0 running/enabled 2090650862
# PM_BR_MPRED_CCACHE: result          1 running/enabled 2090648016
# Miss percent 0 %
# OK - Measured branch prediction rates match reported spectre v2 mitigation.
# success: spectre_v2
ok 4 selftests: powerpc/security: spectre_v2
# selftests: powerpc/security: mitigation-patching.sh
# Spawned threads enabling/disabling mitigations ...
# Waiting for timeout ...
# OK
ok 5 selftests: powerpc/security: mitigation-patching.sh

Here's the same thing without the command line option set:

make[1]: Entering directory
'/home/joel/dev/kernels/linus/tools/testing/selftests/powerpc/security'
TAP version 13
1..5
# selftests: powerpc/security: rfi_flush
# test: rfi_flush_test
# tags: git_version:v5.18-rc1-0-g312310928417
# PASS (L1D misses with rfi_flush=0: 47289780 < 95000000) [10/10 pass]
# PASS (L1D misses with rfi_flush=1: 195001301 > 190000000) [10/10 pass]
# success: rfi_flush_test
ok 1 selftests: powerpc/security: rfi_flush
# selftests: powerpc/security: entry_flush
# test: entry_flush_test
# tags: git_version:v5.18-rc1-0-g312310928417
# PASS (L1D misses with entry_flush=0: 63510274 < 95000000) [10/10 pass]
# PASS (L1D misses with entry_flush=1: 195093006 > 190000000) [10/10 pass]
# success: entry_flush_test
ok 2 selftests: powerpc/security: entry_flush
# selftests: powerpc/security: uaccess_flush
# test: uaccess_flush_test
# tags: git_version:v5.18-rc1-0-g312310928417
# PASS (L1D misses with uaccess_flush=0: 62184912 < 95000000) [10/10 pass]
# PASS (L1D misses with uaccess_flush=1: 196018163 > 190000000) [10/10 pass]
# success: uaccess_flush_test
ok 3 selftests: powerpc/security: uaccess_flush
# selftests: powerpc/security: spectre_v2
# test: spectre_v2
# tags: git_version:v5.18-rc1-0-g312310928417
# sysfs reports: 'Mitigation: Software count cache flush (hardware
accelerated), Software link stack flush'
#  PM_BR_PRED_CCACHE: result          0 running/enabled 2016985490
# PM_BR_MPRED_CCACHE: result          1 running/enabled 2016981520
# Miss percent 0 %
# OK - Measured branch prediction rates match reported spectre v2 mitigation.
# success: spectre_v2
ok 4 selftests: powerpc/security: spectre_v2
# selftests: powerpc/security: mitigation-patching.sh
# Spawned threads enabling/disabling mitigations ...
# Waiting for timeout ...
# OK
ok 5 selftests: powerpc/security: mitigation-patching.sh

>
> I suspect some of them might fail, because they have specific knowledge
> of things and might need an update.
>
> cheers