Re: [PATCH v2 1/3] riscv: mm: Use ASID in update_mmu_cache()

[Klara Modin <klarasmodin@gmail.com>]

Hi,

On 2026-07-15 21:20:07 +0800, Xu Lu wrote:
> Only flush TLB entries for the specified mm in update_mmu_cache_range().
> 
> Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
> ---
>  arch/riscv/include/asm/pgtable.h  | 4 +++-
>  arch/riscv/include/asm/tlbflush.h | 5 +++++
>  arch/riscv/mm/tlbflush.c          | 5 -----
>  3 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 5d5756bda82e..9926556099ae 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -568,6 +568,8 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
>  		struct vm_area_struct *vma, unsigned long address,
>  		pte_t *ptep, unsigned int nr)
>  {
> +	unsigned long asid = get_mm_asid(vma->vm_mm);
> +

It seems the old version of this patch is still used (at least in
next-202650716, 15ce1d7c4ddfe0dff00fcaee4ccaeef3efbc62c6), which means
asid is not initialised here. We instead have:

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 5d5756bda82e..755495a542cc 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -568,6 +568,8 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
 		struct vm_area_struct *vma, unsigned long address,
 		pte_t *ptep, unsigned int nr)
 {
+	unsigned long asid;
+
 	/*
 	 * Svvptc guarantees that the new valid pte will be visible within
 	 * a bounded timeframe, so when the uarch does not cache invalid
@@ -583,10 +585,11 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
 	 * Relying on flush_tlb_fix_spurious_fault would suffice, but
 	 * the extra traps reduce performance.  So, eagerly SFENCE.VMA.
 	 */
+	asid = get_mm_asid(vma->vm_mm);
 	while (nr--)
-		local_flush_tlb_page(address + nr * PAGE_SIZE);
-
+		local_flush_tlb_page_asid(address + nr * PAGE_SIZE, asid);
 }
+
 #define update_mmu_cache(vma, addr, ptep) \
 	update_mmu_cache_range(NULL, vma, addr, ptep, 1)
 

This means that patch 2 of this series will use the uninitialised asid
for local_svinval_vma() and I get the same behaviour as before (hang on
initramfs). If I revert the two patches of this series which are in next
and apply this again it's fine.

Regards,
Klara Modin

>  	/*
>  	 * Svvptc guarantees that the new valid pte will be visible within
>  	 * a bounded timeframe, so when the uarch does not cache invalid
> @@ -584,7 +586,7 @@ static inline void update_mmu_cache_range(struct vm_fault *vmf,
>  	 * the extra traps reduce performance.  So, eagerly SFENCE.VMA.
>  	 */
>  	while (nr--)
> -		local_flush_tlb_page(address + nr * PAGE_SIZE);
> +		local_flush_tlb_page_asid(address + nr * PAGE_SIZE, asid);
>  
>  }
>  #define update_mmu_cache(vma, addr, ptep) \
> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> index eed0abc40514..7c2cd5cc92d3 100644
> --- a/arch/riscv/include/asm/tlbflush.h
> +++ b/arch/riscv/include/asm/tlbflush.h
> @@ -15,6 +15,11 @@
>  #define FLUSH_TLB_NO_ASID       ((unsigned long)-1)
>  
>  #ifdef CONFIG_MMU
> +static inline unsigned long get_mm_asid(struct mm_struct *mm)
> +{
> +	return mm ? cntx2asid(atomic_long_read(&mm->context.id)) : FLUSH_TLB_NO_ASID;
> +}
> +
>  static inline void local_flush_tlb_all(void)
>  {
>  	__asm__ __volatile__ ("sfence.vma" : : : "memory");
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index 8404530ec00f..73c226f719c7 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -110,11 +110,6 @@ static void __ipi_flush_tlb_range_asid(void *info)
>  	local_flush_tlb_range_asid(d->start, d->size, d->stride, d->asid);
>  }
>  
> -static inline unsigned long get_mm_asid(struct mm_struct *mm)
> -{
> -	return mm ? cntx2asid(atomic_long_read(&mm->context.id)) : FLUSH_TLB_NO_ASID;
> -}
> -
>  static void __flush_tlb_range(struct mm_struct *mm,
>  			      const struct cpumask *cmask,
>  			      unsigned long start, unsigned long size,
> -- 
> 2.39.5
>