Re: [PATCH] target/riscv: pmp: Fixup TLB size calculation

[Alistair Francis]

On Wed, Oct 12, 2022 at 12:50 PM LIU Zhiwei
<zhiwei_liu@linux.alibaba.com> wrote:
>
> Reviewed-by: LIU Zhiwei<zhiwei_liu@linux.alibaba.com>

Thanks!

>
> By the way, we missed one related patch that once had been picked to 
> riscv-next patch.
>
> The patch v3:
> https://lore.kernel.org/all/ceeb4037-6d17-0a09-f35a-eaf3280339bb@c-sky.com/T/#m183e4430bda408bc3a2b2751aa94eff7fc02e23c

So this was applied but caused boot failures so it was dropped from my
RISC-V tree

>
> The patch v4:
> https://lists.gnu.org/archive/html/qemu-devel/2021-12/msg02854.html

I think I misunderstood this comment [1] as applying to v4 and it
never got applied.

Do you mind resending the patch?

1: 
https://lore.kernel.org/all/ceeb4037-6d17-0a09-f35a-eaf3280339bb@c-sky.com/T/#m5e958d702d9905169a941f2ae59fdf7ac4a02383

Alistair

>
> I think the patch v4 should be taken at the same time with this patch.
>
> Thanks,
> Zhiwei
>
> On 2022/10/12 9:14, Alistair Francis wrote:
> > From: Alistair Francis <alistair.francis@wdc.com>
> >
> > Since commit 4047368938f6 "accel/tcg: Introduce tlb_set_page_full" we
> > have been seeing this assert
> >
> >      ../accel/tcg/cputlb.c:1294: tlb_set_page_with_attrs: Assertion 
> > `is_power_of_2(size)' failed.
> >
> > When running Tock on the OpenTitan machine.
> >
> > The issue is that pmp_get_tlb_size() would return a TLB size that wasn't
> > a power of 2. The size was also smaller then TARGET_PAGE_SIZE.
> >
> > This patch ensures that any TLB size less then TARGET_PAGE_SIZE is
> > rounded down to 1 to ensure it's a valid size.
> >
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> > This is based on advice from Richard:
> > https://patchwork.kernel.org/project/qemu-devel/patch/20221004141051.110653-9-richard.henderson@linaro.org/#25043166
> >
> >   target/riscv/pmp.c | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
> > index ea2b67d947..2b43e399b8 100644
> > --- a/target/riscv/pmp.c
> > +++ b/target/riscv/pmp.c
> > @@ -628,6 +628,18 @@ bool pmp_is_range_in_tlb(CPURISCVState *env, hwaddr 
> > tlb_sa,
> >       }
> >
> >       if (*tlb_size != 0) {
> > +        /*
> > +         * At this point we have a tlb_size that is the smallest possible 
> > size
> > +         * That fits within a TARGET_PAGE_SIZE and the PMP region.
> > +         *
> > +         * If the size is less then TARGET_PAGE_SIZE we drop the size to 1.
> > +         * This means the result isn't cached in the TLB and is only used 
> > for
> > +         * a single translation.
> > +         */
> > +        if (*tlb_size < TARGET_PAGE_SIZE) {
> > +            *tlb_size = 1;
> > +        }
> > +
> >           return true;
> >       }
> >