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[v1,17/36] target/riscv: Set VS bits in mideleg for Hyp extension

Message ID b1313a76928acfe101247e33248f000e1f82f558.1575914822.git.alistair.francis@wdc.com
State New
Headers show
Series Add RISC-V Hypervisor Extension v0.5 | expand

Commit Message

Alistair Francis Dec. 9, 2019, 6:11 p.m. UTC 
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 target/riscv/csr.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Palmer Dabbelt Jan. 8, 2020, 2:07 a.m. UTC | #1 
On Mon, 09 Dec 2019 10:11:24 PST (-0800), Alistair Francis wrote:
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  target/riscv/csr.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index a4b598d49a..fc38c45a7e 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -449,6 +449,9 @@ static int read_mideleg(CPURISCVState *env, int csrno, target_ulong *val)
>  static int write_mideleg(CPURISCVState *env, int csrno, target_ulong val)
>  {
>      env->mideleg = (env->mideleg & ~delegable_ints) | (val & delegable_ints);
> +    if (riscv_has_ext(env, RVH)) {
> +        env->mideleg |= VS_MODE_INTERRUPTS;
> +    }
>      return 0;
>  }

Do you have any idea why?  The spec is explicit that this is the case, but I'm
surprised.

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Alistair Francis Jan. 21, 2020, 11:11 a.m. UTC | #2 
On Wed, Jan 8, 2020 at 12:07 PM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>
> On Mon, 09 Dec 2019 10:11:24 PST (-0800), Alistair Francis wrote:
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> >  target/riscv/csr.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> > index a4b598d49a..fc38c45a7e 100644
> > --- a/target/riscv/csr.c
> > +++ b/target/riscv/csr.c
> > @@ -449,6 +449,9 @@ static int read_mideleg(CPURISCVState *env, int csrno, target_ulong *val)
> >  static int write_mideleg(CPURISCVState *env, int csrno, target_ulong val)
> >  {
> >      env->mideleg = (env->mideleg & ~delegable_ints) | (val & delegable_ints);
> > +    if (riscv_has_ext(env, RVH)) {
> > +        env->mideleg |= VS_MODE_INTERRUPTS;
> > +    }
> >      return 0;
> >  }
>
> Do you have any idea why?  The spec is explicit that this is the case, but I'm
> surprised.

I'm not sure why, maybe to simplfy hardware design?

Alistair

>
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Anup Patel Jan. 21, 2020, 11:29 a.m. UTC | #3 
On Tue, Jan 21, 2020 at 4:43 PM Alistair Francis <alistair23@gmail.com> wrote:
>
> On Wed, Jan 8, 2020 at 12:07 PM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
> >
> > On Mon, 09 Dec 2019 10:11:24 PST (-0800), Alistair Francis wrote:
> > > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > > ---
> > >  target/riscv/csr.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> > > index a4b598d49a..fc38c45a7e 100644
> > > --- a/target/riscv/csr.c
> > > +++ b/target/riscv/csr.c
> > > @@ -449,6 +449,9 @@ static int read_mideleg(CPURISCVState *env, int csrno, target_ulong *val)
> > >  static int write_mideleg(CPURISCVState *env, int csrno, target_ulong val)
> > >  {
> > >      env->mideleg = (env->mideleg & ~delegable_ints) | (val & delegable_ints);
> > > +    if (riscv_has_ext(env, RVH)) {
> > > +        env->mideleg |= VS_MODE_INTERRUPTS;
> > > +    }
> > >      return 0;
> > >  }
> >
> > Do you have any idea why?  The spec is explicit that this is the case, but I'm
> > surprised.
>
> I'm not sure why, maybe to simplfy hardware design?

As-per my understanding, the VS-mode interrupts can be
taken only when V=1 and these are injected by HS-mode
using HIP CSR.

If we allow VS-mode interrupts to be taken in M-mode then
it means HS-mode can now inject interrupts for M-mode using
HIP CSR. This cannot be allowed hence VS-mode interrupts
are force delegated to S-mode in MIDELEG.

Regards,
Anup
diff mbox series

Patch

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index a4b598d49a..fc38c45a7e 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -449,6 +449,9 @@  static int read_mideleg(CPURISCVState *env, int csrno, target_ulong *val)
 static int write_mideleg(CPURISCVState *env, int csrno, target_ulong val)
 {
     env->mideleg = (env->mideleg & ~delegable_ints) | (val & delegable_ints);
+    if (riscv_has_ext(env, RVH)) {
+        env->mideleg |= VS_MODE_INTERRUPTS;
+    }
     return 0;
 }