| Message ID | 20240109143804.1118307-1-peter.maydell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | target/arm: arm_pamax() no longer needs to do feature propagation | expand |
On 1/10/24 01:38, Peter Maydell wrote: > In arm_pamax(), we need to cope with the virt board calling this > function on a CPU object which has been inited but not realize. > We used to do propagation of feature-flag implications (such as > "V7VE implies LPAE") at realize, so we have some code in arm_pamax() > which manually checks for both V7VE and LPAE feature flags. > > In commit b8f7959f28c4f36 we moved the feature propagation for > almost all features from realize to post-init. That means that > now when the virt board calls arm_pamax(), the feature propagation > has been done. So we can drop the manual propagation handling > and check only for the feature we actually care about, which > is ARM_FEATURE_LPAE. > > Retain the comment that the virt board is calling this function > with a not completely realized CPU object, because that is a > potential beartrap for later changes which is worth calling out. > > (Note that b8f7959f28c4f36 actually fixed a bug in the arm_pamax() > handling: arm_pamax() was missing a check for ARM_FEATURE_V8, so it > incorrectly thought that the qemu-system-arm 'max' CPU did not have > LPAE and turned off 'highmem' support in the virt board. Following > b8f7959f28c4f36 qemu-system-arm 'max' is treated the same as > 'cortex-a15' and other v7 LPAE CPUs, because the generic feature > propagation code does correctly propagate V8 -> V7VE -> LPAE.) > > Signed-off-by: Peter Maydell<peter.maydell@linaro.org> > --- > target/arm/ptw.c | 14 ++++++-------- > 1 file changed, 6 insertions(+), 8 deletions(-) Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
diff --git a/target/arm/ptw.c b/target/arm/ptw.c index 1762b058aec..0da1caae117 100644 --- a/target/arm/ptw.c +++ b/target/arm/ptw.c @@ -95,7 +95,10 @@ static const uint8_t pamax_map[] = { [6] = 52, }; -/* The cpu-specific constant value of PAMax; also used by hw/arm/virt. */ +/* + * The cpu-specific constant value of PAMax; also used by hw/arm/virt. + * Note that machvirt_init calls this on a CPU that is inited but not realized! + */ unsigned int arm_pamax(ARMCPU *cpu) { if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) { @@ -110,13 +113,8 @@ unsigned int arm_pamax(ARMCPU *cpu) return pamax_map[parange]; } - /* - * In machvirt_init, we call arm_pamax on a cpu that is not fully - * initialized, so we can't rely on the propagation done in realize. - */ - if (arm_feature(&cpu->env, ARM_FEATURE_LPAE) || - arm_feature(&cpu->env, ARM_FEATURE_V7VE)) { - /* v7 with LPAE */ + if (arm_feature(&cpu->env, ARM_FEATURE_LPAE)) { + /* v7 or v8 with LPAE */ return 40; } /* Anything else */
In arm_pamax(), we need to cope with the virt board calling this function on a CPU object which has been inited but not realize. We used to do propagation of feature-flag implications (such as "V7VE implies LPAE") at realize, so we have some code in arm_pamax() which manually checks for both V7VE and LPAE feature flags. In commit b8f7959f28c4f36 we moved the feature propagation for almost all features from realize to post-init. That means that now when the virt board calls arm_pamax(), the feature propagation has been done. So we can drop the manual propagation handling and check only for the feature we actually care about, which is ARM_FEATURE_LPAE. Retain the comment that the virt board is calling this function with a not completely realized CPU object, because that is a potential beartrap for later changes which is worth calling out. (Note that b8f7959f28c4f36 actually fixed a bug in the arm_pamax() handling: arm_pamax() was missing a check for ARM_FEATURE_V8, so it incorrectly thought that the qemu-system-arm 'max' CPU did not have LPAE and turned off 'highmem' support in the virt board. Following b8f7959f28c4f36 qemu-system-arm 'max' is treated the same as 'cortex-a15' and other v7 LPAE CPUs, because the generic feature propagation code does correctly propagate V8 -> V7VE -> LPAE.) Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- target/arm/ptw.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)