Re: [PATCH -fixes v2 4/4] riscv: Save/restore envcfg CSR during CPU suspend

[Stefan O'Rear]

On Tue, Feb 13, 2024, at 9:49 AM, Andrew Jones wrote:
> On Mon, Feb 12, 2024 at 07:37:35PM -0800, Samuel Holland wrote:
>> The value of the [ms]envcfg CSR is lost when entering a nonretentive
>> idle state, so the CSR must be rewritten when resuming the CPU.
>> 
>> Cc: <stable@xxxxxxxxxxxxxxx> # v6.7+
>> Fixes: 43c16d51a19b ("RISC-V: Enable cbo.zero in usermode")
>> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
>> ---
>> 
>> Changes in v2:
>>  - Check for privileged ISA v1.12 instead of the specific CSR
>>  - Use riscv_has_extension_likely() instead of new ALTERNATIVE()s
>> 
>>  arch/riscv/include/asm/suspend.h | 1 +
>>  arch/riscv/kernel/suspend.c      | 4 ++++
>>  2 files changed, 5 insertions(+)
>> 
>> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
>> index 02f87867389a..491296a335d0 100644
>> --- a/arch/riscv/include/asm/suspend.h
>> +++ b/arch/riscv/include/asm/suspend.h
>> @@ -14,6 +14,7 @@ struct suspend_context {
>>  	struct pt_regs regs;
>>  	/* Saved and restored by high-level functions */
>>  	unsigned long scratch;
>> +	unsigned long envcfg;
>>  	unsigned long tvec;
>>  	unsigned long ie;
>>  #ifdef CONFIG_MMU
>> diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
>> index 239509367e42..be03615486ed 100644
>> --- a/arch/riscv/kernel/suspend.c
>> +++ b/arch/riscv/kernel/suspend.c
>> @@ -15,6 +15,8 @@
>>  void suspend_save_csrs(struct suspend_context *context)
>>  {
>>  	context->scratch = csr_read(CSR_SCRATCH);
>> +	if (riscv_has_extension_likely(RISCV_ISA_EXT_Sx1p12))
>> +		context->envcfg = csr_read(CSR_ENVCFG);
>>  	context->tvec = csr_read(CSR_TVEC);
>>  	context->ie = csr_read(CSR_IE);
>>  
>> @@ -36,6 +38,8 @@ void suspend_save_csrs(struct suspend_context *context)
>>  void suspend_restore_csrs(struct suspend_context *context)
>>  {
>>  	csr_write(CSR_SCRATCH, context->scratch);
>> +	if (riscv_has_extension_likely(RISCV_ISA_EXT_Sx1p12))
>> +		csr_write(CSR_ENVCFG, context->envcfg);
>>  	csr_write(CSR_TVEC, context->tvec);
>>  	csr_write(CSR_IE, context->ie);
>>  
>> -- 
>> 2.43.0
>>
>
> We're still exposing Zicboz to userspace in hwprobe when only
> RISCV_ISA_EXT_ZICBOZ is present, which will be the case for anything that
> either doesn't implement 1.12, but does implement Zicboz, or maybe does
> implement 1.12, but hasn't started putting Ss1p12 in its ISA string yet
> (e.g. QEMU). We should either stop exposing Zicboz to userspace in those
> cases (since it won't work) or rethink how we want to determine whether
> or not we have envcfg CSRs.

opensbi treats the existence of menvcfg as sufficient evidence to prove that
the hart supports 1.12.  I wouldn't object to having Zicboz imply Ss1p12/Sm1p12.

-s

> Thanks,
> drew
>
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