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Re: [Qemu-arm] [PATCH v2 3/3] target-arm: Implement the S2 MMU inputsize
From: |
Alex Bennée |
Subject: |
Re: [Qemu-arm] [PATCH v2 3/3] target-arm: Implement the S2 MMU inputsize > pamax check |
Date: |
Fri, 22 Jan 2016 11:45:57 +0000 |
User-agent: |
mu4e 0.9.16; emacs 25.0.50.5 |
Edgar E. Iglesias <address@hidden> writes:
> On Fri, Jan 22, 2016 at 10:28:43AM +0000, Alex Bennée wrote:
>>
>> Edgar E. Iglesias <address@hidden> writes:
>>
>> > From: "Edgar E. Iglesias" <address@hidden>
>> >
>> > Implement the inputsize > pamax check for Stage 2 translations.
>> > We have multiple choices for how to respond to errors and
>> > choose to fault.
>> >
>> > Signed-off-by: Edgar E. Iglesias <address@hidden>
>> > ---
>> > target-arm/helper.c | 16 ++++++++++++----
>> > 1 file changed, 12 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/target-arm/helper.c b/target-arm/helper.c
>> > index 4abeb4d..9a7ff5e 100644
>> > --- a/target-arm/helper.c
>> > +++ b/target-arm/helper.c
>> > @@ -6808,7 +6808,7 @@ static bool get_phys_addr_lpae(CPUARMState *env,
>> > target_ulong address,
>> > */
>> > int startlevel = extract32(tcr->raw_tcr, 6, 2);
>> > unsigned int pamax = arm_pamax(cpu);
>> > - bool ok;
>> > + bool ok = true;
>> >
>> > if (va_size == 32 || stride == 9) {
>> > /* AArch32 or 4KB pages */
>> > @@ -6818,9 +6818,17 @@ static bool get_phys_addr_lpae(CPUARMState *env,
>> > target_ulong address,
>> > level = 3 - startlevel;
>> > }
>> >
>> > - /* Check that the starting level is valid. */
>> > - ok = check_s2_startlevel(cpu, va_size == 64, level,
>> > - inputsize, stride, pamax);
>> > + if (va_size == 64 &&
>> > + inputsize > pamax &&
>> > + (arm_el_is_aa64(env, 1) || inputsize > 40)) {
>>
>> If va_size == 64 doesn't that imply arm_el_is_aa64(env, 1)? Looking
>> further up the function it seems that is what sets va_size in the first
>> place. I think that makes the inputsize > 40 check redundant.
>
> va_size == 64 is true if the EL corresponding to the translation _regime_
> is in 64 bit mode (in this case EL2).
>
> EL1 may very well be in 32bit mode.
Ahh yes, I missed that on the first reading. I think it might be clearer
when reading the code to have the:
bool is_aarch64_regime = (va_size == 64);
And use that to make it clear. And then comment on later check that it's
incompatible with EL1 being aarch32.
>
>>
>> > + /* We have multiple choices but choose to fault. */
>> > + ok = false;
>> > + }
>> > + if (ok) {
>> > + /* Check that the starting level is valid. */
>> > + ok = check_s2_startlevel(cpu, va_size == 64, level,
>> > + inputsize, stride, pamax);
>> > + }
>> > if (!ok) {
>> > /* AArch64 reports these as level 0 faults.
>> > * AArch32 reports these as level 1 faults.
>>
>> I'm not a fan of the ok = true / ok = false / ok =
>> check_s2_start_level() / if (!ok) ping-pong here as it is hard to
>> follow. I'm not sure how you could make it cleaner to follow though.
>> Maybe something like:
>>
>> /* For stage 2 translations the starting level is specified by the
>> * VTCR_EL2.SL0 field (whose interpretation depends on the page size)
>> */
>> int startlevel = extract32(tcr->raw_tcr, 6, 2);
>> unsigned int pamax = arm_pamax(cpu);
>> bool is_aarch64_regime = (va_size == 64);
>> bool ok;
>>
>> if (va_size == 32 || stride == 9) {
>> /* AArch32 or 4KB pages */
>> level = 2 - startlevel;
>> } else {
>> /* 16KB or 64KB pages */
>> level = 3 - startlevel;
>> }
>>
>> if (is_aarch64_regime &&
>> inputsize > pamax) {
>> /* We have multiple choices but choose to fault. */
>> ok = false;
>> } else {
>> /* Check that the starting level is valid. */
>> ok = check_s2_startlevel(cpu, is_aarch64_regime, level,
>> inputsize, stride, pamax);
>> }
>> if (!ok) {
>> /* AArch64 reports these as level 0 faults.
>> * AArch32 reports these as level 1 faults.
>> */
>> level = is_aarch64_regime ? 0 : 1;
>> fault_type = translation_fault;
>> goto do_fault;
>> }
>>
>> But I'm wondering if it just makes more sense to push the:
>>
>> is_aarch64_regime && inputsize > pamax
>>
>> Check into check_s2_startlevel? Then you could just have a simple call
>> which succeeds or falls through to a fault?
>
> Yeah, I guess we could rename check_s2_startlevel to something more generic
> and move all the checks there. I don't feel very strongly about either way...
I think it would be cleaner to follow. get_phys_addr_lpae is already a
bit of a monster so the less conditions to keep track of while reading
it the better IMHO.
> Thanks,
> Edgar
>
>
>
>>
>> /* Check that the starting level is valid. */
>> if (!check_s2_startlevel(cpu, is_aarch64_regime, level,
>> inputsize, stride, pamax) ){
>> /* AArch64 reports these as level 0 faults.
>> * AArch32 reports these as level 1 faults.
>> */
>> level = is_aarch64_regime ? 0 : 1;
>> fault_type = translation_fault;
>> goto do_fault;
>> }
>>
>> --
>> Alex Bennée
--
Alex Bennée
[Qemu-arm] [PATCH v2 2/3] target-arm: Make pamax an argument to check_s2_startlevel, Edgar E. Iglesias, 2016/01/21