[Qemu-devel] [PATCHv3 1/5] RISC-V: Only Check PMP if MMU translation succeeds

[Qemu-devel] [PATCHv3 1/5] RISC-V: Only Check PMP if MMU translation succeeds

[Hesham Almatary]

The current implementation unnecessarily checks for PMP even if MMU translation
failed. This may trigger a wrong PMP access exception instead of
a page exception.

For example, the very first instruction fetched after the first satp write in
S-Mode will trigger a PMP access fault instead of an instruction fetch page
fault.

This patch prioritises MMU exceptions over PMP exceptions and only checks for
PMP if MMU translation succeeds. This patch is required for future commits
that properly report PMP exception violations if PTW succeeds.

Signed-off-by: Hesham Almatary <Hesham.Almatary@cl.cam.ac.uk>
---
 target/riscv/cpu_helper.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 41d6db41c3..40fb47e794 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -401,6 +401,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
                   " prot %d\n", __func__, address, ret, pa, prot);

     if (riscv_feature(env, RISCV_FEATURE_PMP) &&
+        (ret == TRANSLATE_SUCCESS) &&
         !pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type)) {
         ret = TRANSLATE_FAIL;
     }
--
2.17.1

Re: [Qemu-devel] [PATCHv3 1/5] RISC-V: Only Check PMP if MMU translation succeeds

[Alistair Francis]

On Wed, May 22, 2019 at 2:13 AM Hesham Almatary
<Hesham.Almatary@cl.cam.ac.uk> wrote:
>
> The current implementation unnecessarily checks for PMP even if MMU translation
> failed. This may trigger a wrong PMP access exception instead of
> a page exception.
>
> For example, the very first instruction fetched after the first satp write in
> S-Mode will trigger a PMP access fault instead of an instruction fetch page
> fault.
>
> This patch prioritises MMU exceptions over PMP exceptions and only checks for
> PMP if MMU translation succeeds. This patch is required for future commits
> that properly report PMP exception violations if PTW succeeds.
>
> Signed-off-by: Hesham Almatary <Hesham.Almatary@cl.cam.ac.uk>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_helper.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 41d6db41c3..40fb47e794 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -401,6 +401,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
>                    " prot %d\n", __func__, address, ret, pa, prot);
>
>      if (riscv_feature(env, RISCV_FEATURE_PMP) &&
> +        (ret == TRANSLATE_SUCCESS) &&
>          !pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type)) {
>          ret = TRANSLATE_FAIL;
>      }
> --
> 2.17.1
>
>

Re: [Qemu-devel] [PATCHv3 1/5] RISC-V: Only Check PMP if MMU translation succeeds

[Alistair Francis]

On Tue, May 21, 2019 at 3:44 AM Hesham Almatary
<Hesham.Almatary@cl.cam.ac.uk> wrote:
>
> The current implementation unnecessarily checks for PMP even if MMU translation
> failed. This may trigger a wrong PMP access exception instead of
> a page exception.
>
> For example, the very first instruction fetched after the first satp write in
> S-Mode will trigger a PMP access fault instead of an instruction fetch page
> fault.
>
> This patch prioritises MMU exceptions over PMP exceptions and only checks for
> PMP if MMU translation succeeds.

It's probably worth noting in the commit message that this commit is
only required for the future commits. Otherwise it is a little
confusing.

Alistair

>
> Signed-off-by: Hesham Almatary <Hesham.Almatary@cl.cam.ac.uk>
> ---
>  target/riscv/cpu_helper.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 41d6db41c3..40fb47e794 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -401,6 +401,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
>                    " prot %d\n", __func__, address, ret, pa, prot);
>
>      if (riscv_feature(env, RISCV_FEATURE_PMP) &&
> +        (ret == TRANSLATE_SUCCESS) &&
>          !pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type)) {
>          ret = TRANSLATE_FAIL;
>      }
> --
> 2.17.1
>
>

[Qemu-devel] [PATCHv3 1/5] RISC-V: Only Check PMP if MMU translation succeeds

[Hesham Almatary]

The current implementation unnecessarily checks for PMP even if MMU translation
failed. This may trigger a wrong PMP access exception instead of
a page exception.

For example, the very first instruction fetched after the first satp write in
S-Mode will trigger a PMP access fault instead of an instruction fetch page
fault.

This patch prioritises MMU exceptions over PMP exceptions and only checks for
PMP if MMU translation succeeds.

Signed-off-by: Hesham Almatary <Hesham.Almatary@cl.cam.ac.uk>
---
 target/riscv/cpu_helper.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 41d6db41c3..40fb47e794 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -401,6 +401,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
                   " prot %d\n", __func__, address, ret, pa, prot);

     if (riscv_feature(env, RISCV_FEATURE_PMP) &&
+        (ret == TRANSLATE_SUCCESS) &&
         !pmp_hart_has_privs(env, pa, TARGET_PAGE_SIZE, 1 << access_type)) {
         ret = TRANSLATE_FAIL;
     }
--
2.17.1