Re: [Qemu-devel] [PATCH v2 3/3] target/arm: Flush only the TLBs affected by TTBR*_EL1

[Richard Henderson <richard.henderson@linaro.org>]

On 10/19/18 7:28 AM, Peter Maydell wrote:
> On 19 October 2018 at 02:56, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>> Only the EL0 and EL1 TLBs are affected by the EL1 register,
>> so flush only 2 of the 8 TLBs.
>>
>> In testing a boot of the Ubuntu installer to the first menu, this
>> accounts for nearly all of the full tlb flushes: all but 11k of
>> the 1.2M instances without the patch.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  target/arm/helper.c | 16 +++++++++-------
>>  1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/target/arm/helper.c b/target/arm/helper.c
>> index ed70ac645e..3ba8e66487 100644
>> --- a/target/arm/helper.c
>> +++ b/target/arm/helper.c
>> @@ -2706,14 +2706,16 @@ static void vmsa_tcr_el1_write(CPUARMState *env, const ARMCPRegInfo *ri,
>>      tcr->raw_tcr = value;
>>  }
>>
>> -static void vmsa_ttbr_write(CPUARMState *env, const ARMCPRegInfo *ri,
>> -                            uint64_t value)
>> +static void vmsa_ttbr_el1_write(CPUARMState *env, const ARMCPRegInfo *ri,
>> +                                uint64_t value)
>>  {
>>      /* If the ASID changes (with a 64-bit write), we must flush the TLB.  */
>>      if (cpreg_field_is_64bit(ri) &&
>>          extract64(raw_read(env, ri) ^ value, 48, 16) != 0) {
>>          ARMCPU *cpu = arm_env_get_cpu(env);
>> -        tlb_flush(CPU(cpu));
>> +        tlb_flush_by_mmuidx(CPU(cpu),
>> +                            ARMMMUIdxBit_S12NSE1 |
>> +                            ARMMMUIdxBit_S12NSE0);
> 
> This isn't taking account of the possibility of secure mode.
> ARMMMUIdxBit_S1SE0 and ARMMMUIdxBit_S1SE1 might also be affected.

Ah.  Is there an easy way to tell if secure mode is present/enabled?  It'd be
nice to not flush tlbs that aren't in use...

> And for AArch32, this writefn is used for the secure-banked versions
> of TTBR0/TTBR1, which means ARMMMUIdxBit_S1E3 may also need flushing.

For aarch32, we don't have an asid, and so do not flush at all.


r~