2024-03-13 10:30:28

by Wang, Xiao W

Subject: [PATCH] riscv: uaccess: Allow the last potential unrolled copy

When the dst buffer pointer points to the last accessible aligned addr, we
could still run another iteration of unrolled copy.

Signed-off-by: Xiao Wang <[email protected]>
---
arch/riscv/lib/uaccess.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index 2e665f8f8fcc..1399d797d81b 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -103,7 +103,7 @@ SYM_FUNC_START(fallback_scalar_usercopy)
fixup REG_S t4, 7*SZREG(a0), 10f
addi a0, a0, 8*SZREG
addi a1, a1, 8*SZREG
- bltu a0, t0, 2b
+ bleu a0, t0, 2b

addi t0, t0, 8*SZREG /* revert to original value */
j .Lbyte_copy_tail
--
2.25.1

2024-05-03 12:16:45

by Alexandre Ghiti

Subject: Re: [PATCH] riscv: uaccess: Allow the last potential unrolled copy

Hi Xiao,

On 13/03/2024 11:33, Xiao Wang wrote:
> When the dst buffer pointer points to the last accessible aligned addr, we
> could still run another iteration of unrolled copy.
>
> Signed-off-by: Xiao Wang <[email protected]>
> ---
> arch/riscv/lib/uaccess.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
> index 2e665f8f8fcc..1399d797d81b 100644
> --- a/arch/riscv/lib/uaccess.S
> +++ b/arch/riscv/lib/uaccess.S
> @@ -103,7 +103,7 @@ SYM_FUNC_START(fallback_scalar_usercopy)
> fixup REG_S t4, 7*SZREG(a0), 10f
> addi a0, a0, 8*SZREG
> addi a1, a1, 8*SZREG
> - bltu a0, t0, 2b
> + bleu a0, t0, 2b
>
> addi t0, t0, 8*SZREG /* revert to original value */
> j .Lbyte_copy_tail


I agree it is still safe to continue for another word_copy here.

Reviewed-by: Alexandre Ghiti <[email protected]>

Thanks,

Alex

2024-05-03 13:04:40

by Alexandre Ghiti

Subject: Re: [PATCH] riscv: uaccess: Allow the last potential unrolled copy

Hi Ben,

On 03/05/2024 14:19, Ben Dooks wrote:
> On 03/05/2024 13:16, Alexandre Ghiti wrote:
>> Hi Xiao,
>>
>> On 13/03/2024 11:33, Xiao Wang wrote:
>>> When the dst buffer pointer points to the last accessible aligned
>>> addr, we
>>> could still run another iteration of unrolled copy.
>>>
>>> Signed-off-by: Xiao Wang <[email protected]>
>>> ---
>>>   arch/riscv/lib/uaccess.S | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
>>> index 2e665f8f8fcc..1399d797d81b 100644
>>> --- a/arch/riscv/lib/uaccess.S
>>> +++ b/arch/riscv/lib/uaccess.S
>>> @@ -103,7 +103,7 @@ SYM_FUNC_START(fallback_scalar_usercopy)
>>>       fixup REG_S   t4,  7*SZREG(a0), 10f
>>>       addi    a0, a0, 8*SZREG
>>>       addi    a1, a1, 8*SZREG
>>> -    bltu    a0, t0, 2b
>>> +    bleu    a0, t0, 2b
>>>       addi    t0, t0, 8*SZREG /* revert to original value */
>>>       j    .Lbyte_copy_tail
>>
>>
>> I agree it is still safe to continue for another word_copy here.
>>
>> Reviewed-by: Alexandre Ghiti <[email protected]>
>
> Out of interest, has anyone checked if causing a schedule event during
> this code breaks like the last time we had issues with the upstream
> testing?


I vaguely remember something, do you have a link to that discussion by
chance?


>
> I did propose saving the state of the user-access flag in the task
> struct


Makes sense, I just took a quick look and SR_SUM is cleared as soon as
we enter handle_exception() and it does not seem to be restored. Weird
it works, unless I missed something!


> but we mostly solved it by making sleeping functions stay
> away from the address calculation. This of course may have been done
> already or need to be done if three's long areas where the user-access
> flags can be disabled (generally only a few drivers did this, so we
> may not have come across the problem)
>
I don't understand what you mean here, would you mind expanding a bit?

Thanks,

Alex