linux-kernel - Re: [PATCH v4 08/12] riscv: mm: Introduce cntx2asid/cntx2version helper macros

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Message-ID: <057f7d38-08b7-4693-907c-b2efa6a75a22@sifive.com>
Date: Thu, 4 Jan 2024 09:42:47 -0600
From: Samuel Holland <samuel.holland@...ive.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Palmer Dabbelt <palmer@...belt.com>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 08/12] riscv: mm: Introduce cntx2asid/cntx2version
 helper macros

Hi Alex,

On 2024-01-04 6:39 AM, Alexandre Ghiti wrote:
> On Tue, Jan 2, 2024 at 11:01 PM Samuel Holland
> <samuel.holland@...ive.com> wrote:
>>
>> When using the ASID allocator, the MM context ID contains two values:
>> the ASID in the lower bits, and the allocator version number in the
>> remaining bits. Use macros to make this separation more obvious.
>>
>> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
>> ---
>>
>> (no changes since v1)
>>
>>  arch/riscv/include/asm/mmu.h |  3 +++
>>  arch/riscv/mm/context.c      | 12 ++++++------
>>  arch/riscv/mm/tlbflush.c     |  2 +-
>>  3 files changed, 10 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
>> index 355504b37f8e..a550fbf770be 100644
>> --- a/arch/riscv/include/asm/mmu.h
>> +++ b/arch/riscv/include/asm/mmu.h
>> @@ -26,6 +26,9 @@ typedef struct {
>>  #endif
>>  } mm_context_t;
>>
>> +#define cntx2asid(cntx)                ((cntx) & asid_mask)
>> +#define cntx2version(cntx)     ((cntx) & ~asid_mask)
> 
> Not a big fan of the naming, I would have something like
> get_asid_from_context() and get_version_from_context() or something
> like that, but up to you of course.

Thanks for the review. I'm not really a fan of it either, but I tried to match
precedent from other architectures. These loosely follow the naming of
ctxid2asid() from arm64 and idx2asid() from csky. arm uses ASID().

Regards,
Samuel

>> +
>>  void __init create_pgd_mapping(pgd_t *pgdp, uintptr_t va, phys_addr_t pa,
>>                                phys_addr_t sz, pgprot_t prot);
>>  #endif /* __ASSEMBLY__ */
>> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
>> index 217fd4de6134..43d005f63253 100644
>> --- a/arch/riscv/mm/context.c
>> +++ b/arch/riscv/mm/context.c
>> @@ -81,7 +81,7 @@ static void __flush_context(void)
>>                 if (cntx == 0)
>>                         cntx = per_cpu(reserved_context, i);
>>
>> -               __set_bit(cntx & asid_mask, context_asid_map);
>> +               __set_bit(cntx2asid(cntx), context_asid_map);
>>                 per_cpu(reserved_context, i) = cntx;
>>         }
>>
>> @@ -102,7 +102,7 @@ static unsigned long __new_context(struct mm_struct *mm)
>>         lockdep_assert_held(&context_lock);
>>
>>         if (cntx != 0) {
>> -               unsigned long newcntx = ver | (cntx & asid_mask);
>> +               unsigned long newcntx = ver | cntx2asid(cntx);
>>
>>                 /*
>>                  * If our current CONTEXT was active during a rollover, we
>> @@ -115,7 +115,7 @@ static unsigned long __new_context(struct mm_struct *mm)
>>                  * We had a valid CONTEXT in a previous life, so try to
>>                  * re-use it if possible.
>>                  */
>> -               if (!__test_and_set_bit(cntx & asid_mask, context_asid_map))
>> +               if (!__test_and_set_bit(cntx2asid(cntx), context_asid_map))
>>                         return newcntx;
>>         }
>>
>> @@ -168,7 +168,7 @@ static void set_mm_asid(struct mm_struct *mm, unsigned int cpu)
>>          */
>>         old_active_cntx = atomic_long_read(&per_cpu(active_context, cpu));
>>         if (old_active_cntx &&
>> -           ((cntx & ~asid_mask) == atomic_long_read(&current_version)) &&
>> +           (cntx2version(cntx) == atomic_long_read(&current_version)) &&
>>             atomic_long_cmpxchg_relaxed(&per_cpu(active_context, cpu),
>>                                         old_active_cntx, cntx))
>>                 goto switch_mm_fast;
>> @@ -177,7 +177,7 @@ static void set_mm_asid(struct mm_struct *mm, unsigned int cpu)
>>
>>         /* Check that our ASID belongs to the current_version. */
>>         cntx = atomic_long_read(&mm->context.id);
>> -       if ((cntx & ~asid_mask) != atomic_long_read(&current_version)) {
>> +       if (cntx2version(cntx) != atomic_long_read(&current_version)) {
>>                 cntx = __new_context(mm);
>>                 atomic_long_set(&mm->context.id, cntx);
>>         }
>> @@ -191,7 +191,7 @@ static void set_mm_asid(struct mm_struct *mm, unsigned int cpu)
>>
>>  switch_mm_fast:
>>         csr_write(CSR_SATP, virt_to_pfn(mm->pgd) |
>> -                 ((cntx & asid_mask) << SATP_ASID_SHIFT) |
>> +                 (cntx2asid(cntx) << SATP_ASID_SHIFT) |
>>                   satp_mode);
>>
>>         if (need_flush_tlb)
>> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
>> index 76b24d4ed4ab..5ec621545c69 100644
>> --- a/arch/riscv/mm/tlbflush.c
>> +++ b/arch/riscv/mm/tlbflush.c
>> @@ -85,7 +85,7 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
>>                         return;
>>
>>                 if (static_branch_unlikely(&use_asid_allocator))
>> -                       asid = atomic_long_read(&mm->context.id) & asid_mask;
>> +                       asid = cntx2asid(atomic_long_read(&mm->context.id));
>>         } else {
>>                 cmask = cpu_online_mask;
>>         }
>> --
>> 2.42.0
>>
> 
> You can add:
> 
> Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>
> 
> Thanks,
> 
> Alex