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Re: [PATCH] target/arm: Don't get MDCR_EL2 in pmu_counter_enabled() befo


From: Richard Henderson
Subject: Re: [PATCH] target/arm: Don't get MDCR_EL2 in pmu_counter_enabled() before checking ARM_FEATURE_PMU
Date: Sat, 10 Feb 2024 07:45:30 -1000
User-agent: Mozilla Thunderbird

On 2/8/24 05:33, Peter Maydell wrote:
It doesn't make sense to read the value of MDCR_EL2 on a non-A-profile
CPU, and in fact if you try to do it we will assert:

#6  0x00007ffff4b95e96 in __GI___assert_fail
     (assertion=0x5555565a8c70 "!arm_feature(env, ARM_FEATURE_M)",
file=0x5555565a6e5c "../../target/arm/helper.c", line=12600,
function=0x5555565a9560 <__PRETTY_FUNCTION__.0>
"arm_security_space_below_el3") at ./assert/assert.c:101
#7  0x0000555555ebf412 in arm_security_space_below_el3
(env=0x555557bc8190) at ../../target/arm/helper.c:12600
#8  0x0000555555ea6f89 in arm_is_el2_enabled (env=0x555557bc8190) at
../../target/arm/cpu.h:2595
#9  0x0000555555ea942f in arm_mdcr_el2_eff (env=0x555557bc8190) at
../../target/arm/internals.h:1512

We might call pmu_counter_enabled() on an M-profile CPU (for example
from the migration pre/post hooks in machine.c); this should always
return false because these CPUs don't set ARM_FEATURE_PMU.

Avoid the assertion by not calling arm_mdcr_el2_eff() before we
have done the early return for "PMU not present".

This fixes an assertion failure if you try to do a loadvm or
savevm for an M-profile board.

Cc:qemu-stable@nongnu.org
Resolves:https://gitlab.com/qemu-project/qemu/-/issues/2155
Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
---
  target/arm/helper.c | 12 ++++++++++--
  1 file changed, 10 insertions(+), 2 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~



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