| Message ID | 20240102220134.3229156-12-samuel.holland@sifive.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | riscv: ASID-related and UP-related TLB flush enhancements | expand |
On Tue, Jan 2, 2024 at 11:01 PM Samuel Holland <samuel.holland@sifive.com> wrote: > > If the CPU does not support multiple ASIDs, all MM contexts use ASID 0. > In this case, it is still beneficial to flush the TLB by ASID, as the > single-ASID variant of the sfence.vma instruction preserves TLB entries > for global (kernel) pages. > > This optimization is recommended by the RISC-V privileged specification: > > If the implementation does not provide ASIDs, or software chooses > to always use ASID 0, then after every satp write, software should > execute SFENCE.VMA with rs1=x0. In the common case that no global > translations have been modified, rs2 should be set to a register > other than x0 but which contains the value zero, so that global > translations are not flushed. > > It is not possible to apply this optimization when using the ASID > allocator, because that code must flush the TLB for all ASIDs at once > when incrementing the version number. > > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> > --- > > (no changes since v1) > > arch/riscv/mm/context.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c > index 43a8bc2d5af4..3ca9b653df7d 100644 > --- a/arch/riscv/mm/context.c > +++ b/arch/riscv/mm/context.c > @@ -200,7 +200,7 @@ static void set_mm_noasid(struct mm_struct *mm) > { > /* Switch the page table and blindly nuke entire local TLB */ > csr_write(CSR_SATP, virt_to_pfn(mm->pgd) | satp_mode); > - local_flush_tlb_all(); > + local_flush_tlb_all_asid(0); > } > > static inline void set_mm(struct mm_struct *prev, > -- > 2.42.0 > You can add: Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Thanks, Alex
diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c index 43a8bc2d5af4..3ca9b653df7d 100644 --- a/arch/riscv/mm/context.c +++ b/arch/riscv/mm/context.c @@ -200,7 +200,7 @@ static void set_mm_noasid(struct mm_struct *mm) { /* Switch the page table and blindly nuke entire local TLB */ csr_write(CSR_SATP, virt_to_pfn(mm->pgd) | satp_mode); - local_flush_tlb_all(); + local_flush_tlb_all_asid(0); } static inline void set_mm(struct mm_struct *prev,
If the CPU does not support multiple ASIDs, all MM contexts use ASID 0. In this case, it is still beneficial to flush the TLB by ASID, as the single-ASID variant of the sfence.vma instruction preserves TLB entries for global (kernel) pages. This optimization is recommended by the RISC-V privileged specification: If the implementation does not provide ASIDs, or software chooses to always use ASID 0, then after every satp write, software should execute SFENCE.VMA with rs1=x0. In the common case that no global translations have been modified, rs2 should be set to a register other than x0 but which contains the value zero, so that global translations are not flushed. It is not possible to apply this optimization when using the ASID allocator, because that code must flush the TLB for all ASIDs at once when incrementing the version number. Signed-off-by: Samuel Holland <samuel.holland@sifive.com> --- (no changes since v1) arch/riscv/mm/context.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)