Re: [PATCH v2] target/riscv: fix check of guest pa top bits

[Alistair Francis]

On Tue, May 5, 2020 at 1:40 PM Alistair Francis <address@hidden> wrote:
>
> On Fri, May 1, 2020 at 11:51 AM Jose Martins <address@hidden> wrote:
> >
> > The spec states that on sv39x4 guest physical  "address bits 63:41 must
> > all be zeros, or else a guest-page-fault exception occurs.".  However,
> > the check performed for these top bits of the virtual address on the
> > second stage is the same as the one performed for virtual addresses on
> > the first stage except with the 2-bit extension, effectively creating
> > the same kind of "hole" in the guest's physical address space. I believe
> > the following patch fixes this issue:
> >
> > Signed-off-by: Jose Martins <address@hidden>
>
> Reviewed-by: Alistair Francis <address@hidden>
>
> Applied to RISC-V tree.

This breaks 32-bit Hypervisors, can you look into it?

Alistair

>
> Alistair
>
> > ---
> >  target/riscv/cpu_helper.c | 20 +++++++++++++-------
> >  1 file changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> > index 247304d850..ae22c30bdd 100644
> > --- a/target/riscv/cpu_helper.c
> > +++ b/target/riscv/cpu_helper.c
> > @@ -426,15 +426,21 @@ static int get_physical_address(CPURISCVState *env, 
> > hwaddr *physical,
> >      int va_bits = PGSHIFT + levels * ptidxbits + widened;
> >      target_ulong mask, masked_msbs;
> >
> > -    if (TARGET_LONG_BITS > (va_bits - 1)) {
> > -        mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
> > +    if (!first_stage) {
> > +        if ((addr >> va_bits) != 0) {
> > +            return TRANSLATE_FAIL;
> > +        }
> >      } else {
> > -        mask = 0;
> > -    }
> > -    masked_msbs = (addr >> (va_bits - 1)) & mask;
> > +        if (TARGET_LONG_BITS > (va_bits - 1)) {
> > +            mask = (1L << (TARGET_LONG_BITS - (va_bits - 1))) - 1;
> > +        } else {
> > +            mask = 0;
> > +        }
> > +        masked_msbs = (addr >> (va_bits - 1)) & mask;
> >
> > -    if (masked_msbs != 0 && masked_msbs != mask) {
> > -        return TRANSLATE_FAIL;
> > +        if (masked_msbs != 0 && masked_msbs != mask) {
> > +            return TRANSLATE_FAIL;
> > +        }
> >      }
> >
> >      int ptshift = (levels - 1) * ptidxbits;
> > --
> > 2.25.1
> >
> >