On Wed, 22 May 2019 at 03:25, Jonathan Behrens wrote:
>
> Hesham,
>
> I don't think this is quite right. If I understand correctly, PMP permissions
> are only validated on TLB fills, not on all accesses. (Is anyone able to
> confirm this?) If so, this function can't just validate the range of a single
> access and then place the entire page into the TLB. However, the current code
> is also wrong because an access should succeed/fail based on the permissions
> only for the range it actually touches even regardless of the permissions on
> the rest of the page. Now that I think about it, I'd also expect that
> somewhere in the PMP logic would flush the TLB every time any of the related
> control registers change though I can't find anywhere that this is
> happening...
>
I believe the TLB fill function is called on all accesses, but I might
be wrong. I will wait for someone to confirm otherwise.
It's mentioned in the spec that sfence.vma has to be executed after
changing PMP configs, so it's a SW concern (i.e., not QEMU's).
> Sorry to keep raising complaints about this patch set, the interaction
> between physical memory protection and paging is very subtle. Even some real
> hardware has had errata related to it!
>
> Jonathan
>
> On Tue, May 21, 2019 at 6:33 PM Alistair Francis wrote:
>>
>> On Tue, May 21, 2019 at 3:45 AM Hesham Almatary
>> wrote:
>> >
>> > The PMP check should be of the memory access size rather
>> > than TARGET_PAGE_SIZE.
>> >
>> > Signed-off-by: Hesham Almatary
>>
>> Reviewed-by: Alistair Francis
>>
>> Alistair
>>
>> > ---
>> > target/riscv/cpu_helper.c | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
>> > index d0b0f9cf88..ce1f47e4e3 100644
>> > --- a/target/riscv/cpu_helper.c
>> > +++ b/target/riscv/cpu_helper.c
>> > @@ -410,7 +410,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address,
>> > int size,
>> >
>> > if (riscv_feature(env, RISCV_FEATURE_PMP) &&
>> > (ret == TRANSLATE_SUCCESS) &&
>> > -!pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type))
>> > {
>> > +!pmp_hart_has_privs(env, pa, size, 1 << access_type)) {
>> > ret = TRANSLATE_PMP_FAIL;
>> > }
>> > if (ret == TRANSLATE_PMP_FAIL) {
>> > --
>> > 2.17.1
>> >
>> >
>>
