2022-02-02 09:53:26

by Guo Ren

Subject: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread

From: Guo Ren <[email protected]>

If the current task is in COMPAT mode, set SR_UXL_32 in status for
returning userspace. We need CONFIG _COMPAT to prevent compiling
errors with rv32 defconfig.

Signed-off-by: Guo Ren <[email protected]>
Signed-off-by: Guo Ren <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
---
arch/riscv/kernel/process.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 03ac3aa611f5..1a666ad299b4 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
}
regs->epc = pc;
regs->sp = sp;
+
+#ifdef CONFIG_COMPAT
+ if (is_compat_task())
+ regs->status |= SR_UXL_32;
+#endif
}

void flush_thread(void)
--
2.25.1

2022-02-23 02:39:37

by Palmer Dabbelt

Subject: Re: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread

On Tue, 01 Feb 2022 07:05:37 PST (-0800), [email protected] wrote:
> From: Guo Ren <[email protected]>
>
> If the current task is in COMPAT mode, set SR_UXL_32 in status for
> returning userspace. We need CONFIG _COMPAT to prevent compiling
> errors with rv32 defconfig.
>
> Signed-off-by: Guo Ren <[email protected]>
> Signed-off-by: Guo Ren <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Palmer Dabbelt <[email protected]>
> ---
> arch/riscv/kernel/process.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 03ac3aa611f5..1a666ad299b4 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> }
> regs->epc = pc;
> regs->sp = sp;
> +
> +#ifdef CONFIG_COMPAT
> + if (is_compat_task())
> + regs->status |= SR_UXL_32;

Not sure if I'm just misunderstanding the bit ops here, but aren't we
trying to set the UXL field to 1 (for UXL=32)? That should be a bit
field set op, not just an OR.

> +#endif
> }
>
> void flush_thread(void)

Additionally: this isn't really an issue so much with this patch, but it
does bring up that we're relying on someone else to have set UXL=64 on
CONFIG_COMPAT=n systems. I don't see that in any spec anywhere, so we
should really be setting UXL in Linux for all systems (ie, not just those with
COMPAT=y).

2022-02-24 00:44:43

by Guo Ren

Subject: Re: [PATCH V5 13/21] riscv: compat: process: Add UXL_32 support in start_thread

On Wed, Feb 23, 2022 at 9:42 AM Palmer Dabbelt <[email protected]> wrote:
>
> On Tue, 01 Feb 2022 07:05:37 PST (-0800), [email protected] wrote:
> > From: Guo Ren <[email protected]>
> >
> > If the current task is in COMPAT mode, set SR_UXL_32 in status for
> > returning userspace. We need CONFIG _COMPAT to prevent compiling
> > errors with rv32 defconfig.
> >
> > Signed-off-by: Guo Ren <[email protected]>
> > Signed-off-by: Guo Ren <[email protected]>
> > Cc: Arnd Bergmann <[email protected]>
> > Cc: Palmer Dabbelt <[email protected]>
> > ---
> > arch/riscv/kernel/process.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> > index 03ac3aa611f5..1a666ad299b4 100644
> > --- a/arch/riscv/kernel/process.c
> > +++ b/arch/riscv/kernel/process.c
> > @@ -97,6 +97,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> > }
> > regs->epc = pc;
> > regs->sp = sp;
> > +
> > +#ifdef CONFIG_COMPAT
> > + if (is_compat_task())
> > + regs->status |= SR_UXL_32;
>
> Not sure if I'm just misunderstanding the bit ops here, but aren't we
> trying to set the UXL field to 1 (for UXL=32)? That should be a bit
> field set op, not just an OR.
You are right, I would modify like this:
+ if (is_compat_task())
+ regs->status = （regs->status & ~SR_UXL) | SR_UXL_32;
+ else
+. regs->status = （regs->status & ~SR_UXL) | SR_UXL_64;


>
> > +#endif
> > }
> >
> > void flush_thread(void)
>
> Additionally: this isn't really an issue so much with this patch, but it
> does bring up that we're relying on someone else to have set UXL=64 on
> CONFIG_COMPAT=n systems. I don't see that in any spec anywhere, so we
> should really be setting UXL in Linux for all systems (ie, not just those with
> COMPAT=y).



--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/