Re: RE: [PATCH 2/2] iommupt: Encode IOMMU_MMIO/IOMMU_CACHE via RISC-V Svpbmt bits

[fangyu.yu@linux.alibaba.com]

>> From: fangyu.yu@linux.alibaba.com <fangyu.yu@linux.alibaba.com>
>> Sent: Saturday, April 11, 2026 10:22 AM
>>
>> From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>>
>> When the RISC-V IOMMU page table format support Svpbmt, PBMT provides
>> a way to tag mappings with page-based memory types. Encode memory type
>> via PBMT in RISC-V IOMMU PTEs:
>>
>>   - IOMMU_MMIO   -> PBMT=IO
>>   - !IOMMU_CACHE -> PBMT=NC
>
>In concept IOMMU_CACHE is cleared when IOMMU_MMIO is set. From the
>code PBMT=IO in this case.
>
>So strictly speaking the 2nd line should be:
>
>  - !IOMMU_MMIO && !IOMMU_CACHE -> PBMT=NC
>
>??
>

Agree. I'll clarify the commit message accordingly to avoid implying
that the MMIO case could fall into the NC rule.

>>   - otherwise    -> PBMT=Normal (PBMT=0)
>>
>> Clear the PBMT field before applying the selected encoding, and only
>> touch PBMT when PT_FEAT_RISCV_SVPBMT is advertised.
>>
>> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>> ---
>>  drivers/iommu/generic_pt/fmt/riscv.h | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/iommu/generic_pt/fmt/riscv.h
>> b/drivers/iommu/generic_pt/fmt/riscv.h
>> index a7fef6266a36..02051bb3c6e5 100644
>> --- a/drivers/iommu/generic_pt/fmt/riscv.h
>> +++ b/drivers/iommu/generic_pt/fmt/riscv.h
>> @@ -58,6 +58,8 @@ enum {
>>  	RISCVPT_G = BIT(5),
>>  	RISCVPT_A = BIT(6),
>>  	RISCVPT_D = BIT(7),
>> +	RISCVPT_NC = BIT(61),
>> +	RISCVPT_IO = BIT(62),
>>  	RISCVPT_RSW = GENMASK(9, 8),
>>  	RISCVPT_PPN32 = GENMASK(31, 10),
>
>sort by bit positions
>

Got it, will reorder in v2.

>>
>> @@ -237,6 +239,13 @@ static inline int riscvpt_iommu_set_prot(struct
>> pt_common *common,
>>  		pte |= RISCVPT_R;
>>  	if (!(iommu_prot & IOMMU_NOEXEC))
>>  		pte |= RISCVPT_X;
>> +	if (common->features & BIT(PT_FEAT_RISCV_SVPBMT)) {
>> +		pte &= ~RISCVPT_PBMT;
>
>this is unnecessary due to the earlier assignment:
>
>	pte = RISCVPT_A | RISCVPT_U;
>

As things stand it’s not needed, I'll drop it in v2.

>> +		if (iommu_prot & IOMMU_MMIO)
>> +			pte |= RISCVPT_IO;
>> +		else if (!(iommu_prot & IOMMU_CACHE))
>> +			pte |= RISCVPT_NC;
>> +	}
>>
>>  	/* Caller must specify a supported combination of flags */
>>  	if (unlikely((pte & (RISCVPT_X | RISCVPT_W | RISCVPT_R)) == 0))
>> --
>> 2.50.1

Thanks,
Fangyu

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