lkml.org 
[lkml]   [2022]   [Jul]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3] LoongArch: Remove vcsr in loongarch_fpu


在2022年7月7日七月 上午8:35,Qi Hu写道:
> On 2022/7/7 14:45, Huacai Chen wrote:
>> Hi, all,
>>
>> I have rewritten the commit message. If no problem, this patch will be
>> queued for loongarch-fixes.
>> --
>> The `vcsr` only exists in the old hardware design, it isn't used in any
>> shipped hardware from Loongson-3A5000 on. FPU and LSX/LASX both use the
>> `fcsr` as their control and status registers now. For example, the RM
>> control bit in fcsr0 is shared by FPU, LSX and LASX.
>>
>> Particularly, fcsr16 to fcsr31 are reserved for LSX/LASX now, access to
>> these registers has no visible effect if LSX/LASX is enabled, and will
>> cause SXD/ASXD exceptions if LSX/LASX is not enabled.
>>
>> So, mentions of vcsr are obsolete in the first place, let's remove them.
>
> Or simply say this?
>
> Remove VCSR from "loongarch_fpu" which is used for debugging.

Then you it will be a cross talk vulnerability if you simply ignore it in kernel.

Processes can create a covert channel for surreptitious data exchange based on VCSR like m1racles[1] for apple m1.

Thanks
[1]: https://m1racles.com/

>> --
>> Huacai
>>
>> On Wed, Jul 6, 2022 at 7:29 PM huqi <huqi@loongson.cn> wrote:
>>> From: Qi Hu <huqi@loongson.cn>
>>>
>>> The `vcsr` is not used anymore. Remove this member from `loongarch_fpu`.
>>>
>>> From 3A5000(LoongArch), `vcsr` is removed in hardware. FP and LSX/LASX
>>> both use `fcsr` as their csr.
>>>
>>> Particularly, fcsr from $r16 to $r31 are reserved for LSX/LASX, an
>>> using the registers in this area will cause SXD/ASXD if LSX/LASX is
>>> not enabled.
>>>
>>> Signed-off-by: Qi Hu <huqi@loongson.cn>
>>> ---
>>> V3:
>>> - Modify commit message to conform to the format.
>>> V2:
>>> - Add more details in the commit message.
>>> ---
>>> arch/loongarch/include/asm/fpregdef.h | 1 -
>>> arch/loongarch/include/asm/processor.h | 2 --
>>> arch/loongarch/kernel/asm-offsets.c | 1 -
>>> arch/loongarch/kernel/fpu.S | 10 ----------
>>> 4 files changed, 14 deletions(-)
>>>
>>> diff --git a/arch/loongarch/include/asm/fpregdef.h b/arch/loongarch/include/asm/fpregdef.h
>>> index adb16e4b43b0..b6be527831dd 100644
>>> --- a/arch/loongarch/include/asm/fpregdef.h
>>> +++ b/arch/loongarch/include/asm/fpregdef.h
>>> @@ -48,6 +48,5 @@
>>> #define fcsr1 $r1
>>> #define fcsr2 $r2
>>> #define fcsr3 $r3
>>> -#define vcsr16 $r16
>>>
>>> #endif /* _ASM_FPREGDEF_H */
>>> diff --git a/arch/loongarch/include/asm/processor.h b/arch/loongarch/include/asm/processor.h
>>> index 1d63c934b289..57ec45aa078e 100644
>>> --- a/arch/loongarch/include/asm/processor.h
>>> +++ b/arch/loongarch/include/asm/processor.h
>>> @@ -80,7 +80,6 @@ BUILD_FPR_ACCESS(64)
>>>
>>> struct loongarch_fpu {
>>> unsigned int fcsr;
>>> - unsigned int vcsr;
>>> uint64_t fcc; /* 8x8 */
>>> union fpureg fpr[NUM_FPU_REGS];
>>> };
>>> @@ -161,7 +160,6 @@ struct thread_struct {
>>> */ \
>>> .fpu = { \
>>> .fcsr = 0, \
>>> - .vcsr = 0, \
>>> .fcc = 0, \
>>> .fpr = {{{0,},},}, \
>>> }, \
>>> diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c
>>> index bfb65eb2844f..20cd9e16a95a 100644
>>> --- a/arch/loongarch/kernel/asm-offsets.c
>>> +++ b/arch/loongarch/kernel/asm-offsets.c
>>> @@ -166,7 +166,6 @@ void output_thread_fpu_defines(void)
>>>
>>> OFFSET(THREAD_FCSR, loongarch_fpu, fcsr);
>>> OFFSET(THREAD_FCC, loongarch_fpu, fcc);
>>> - OFFSET(THREAD_VCSR, loongarch_fpu, vcsr);
>>> BLANK();
>>> }
>>>
>>> diff --git a/arch/loongarch/kernel/fpu.S b/arch/loongarch/kernel/fpu.S
>>> index 75c6ce0682a2..a631a7137667 100644
>>> --- a/arch/loongarch/kernel/fpu.S
>>> +++ b/arch/loongarch/kernel/fpu.S
>>> @@ -146,16 +146,6 @@
>>> movgr2fcsr fcsr0, \tmp0
>>> .endm
>>>
>>> - .macro sc_save_vcsr base, tmp0
>>> - movfcsr2gr \tmp0, vcsr16
>>> - EX st.w \tmp0, \base, 0
>>> - .endm
>>> -
>>> - .macro sc_restore_vcsr base, tmp0
>>> - EX ld.w \tmp0, \base, 0
>>> - movgr2fcsr vcsr16, \tmp0
>>> - .endm
>>> -
>>> /*
>>> * Save a thread's fp context.
>>> */
>>> --
>>> 2.36.1
>>>
>>>

--
- Jiaxun

\
 
 \ /
  Last update: 2022-07-07 10:32    [W:0.086 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site