Re: [PATCH v3 5/6] target/arm: Do memory type alignment check when translation disabled

[Peter Maydell]

On Mon, 22 Apr 2024 at 16:48, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 4/22/24 08:26, Clément Chigot wrote:
> > Hi Richard,
> >
> > While testing the future V9, I've some regressions on a custom board
> > using cortex-R5 CPUs.
> > Unaligned data accesses are no longer allowed because of that patch.
> >
> > I've dug into the various documentation and it seems that R-profile
> > CPUs don't have the same default memory type as A-profile. It depends
> > on a default memory map provided in the R-Profile RM in C1.3 [1], even
> > when PMU is disabled.
> >
> >> Each PMSAv8-32 MPU has an associated default memory map which is used when 
> >> the MPU is not enabled.
> >> ...
> >> Table C1-4 and Table C1-5 describe the default memory map defined for the 
> >> EL1 MPU.
> >
> > For our case, Table C1-5 can be simplified as:
> >   |  0x00000000 – 0x7FFFFFFF Normal
> >   |  0x80000000 – 0xBFFFFFFF Device-nGnRE
> >   |  0xC0000000 – 0xFFFFFFFF Device-nGnRnE
> >
> > Therefore, we can't blindly enable strict alignment checking solely on
> > SCTLR bits. We should make it depend on the address targeted. But is
> > it possible to know that address in `aprofile_require_alignment` ?
> > with `mmu_idx` ?
>
> No, this would need to be handled in get_phys_addr_disabled.
>
> > By the way, are R-Profile CPUs the same as those having the `PMSA`
> > feature ? That could mean we can use the `ARM_FEATURE_PMSA` to deal
> > with that, instead of create a new `ARM_FEATURE_R`
>
> No, some armv5 have PMSA.
>
> >
> > Note that the RM I've linked is for ARMv8. But this other link [2]
> > seems to show a similar behavior for arm-v7.
> >
> > cc Jonathan and Ard, though not sure this is the same bug you've
> > reported earlier.
> >
> > Thanks,
> > Clément
> > [1] https://developer.arm.com/documentation/ddi0568/a-c/?lang=en
> > [2] 
> > https://developer.arm.com/documentation/ddi0406/cb/System-Level-Architecture/Protected-Memory-System-Architecture--PMSA-/About-the-PMSA/Enabling-and-disabling-the-MPU?lang=en#BEIJEFCJ
>
> Ouch, thanks for the armv7 link.  At the moment it looks like my blanket 
> mmu-disabled
> change should be restricted to armv8.

Restricted to A-profile, probably. I haven't cross-checked, but IIRC
for v7A this is IMPDEF and we're OK to fault it.

thanks
-- PMM