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Date: Tue, 16 May 2023 21:13:00 +0800
From: WANG Xuerui <kernel@...0n.name>
To: Huacai Chen <chenhuacai@...ngson.cn>,
Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, linux-arch@...r.kernel.org,
Xuefeng Li <lixuefeng@...ngson.cn>,
Guo Ren <guoren@...nel.org>,
Jiaxun Yang <jiaxun.yang@...goat.com>,
linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
Liang Gao <gaoliang@...ngson.cn>, Jun Yi <yijun@...ngson.cn>
Subject: Re: [PATCH] LoongArch: Introduce hardware page table walker
On 2023/5/16 20:46, Huacai Chen wrote:
> Loongson-3A6000 and newer processors have hardware page table walker
> (PTW) support. PTW can handle all fastpaths of TLBI/TLBL/TLBS/TLBM
> exceptions by hardware, software only need to handle slowpaths (page
> faults).
>
> BTW, PTW doesn't append _PAGE_MODIFIED for page table entries, so we
> change pmd_dirty() and pte_dirty() to also check _PAGE_DIRTY for the
> "dirty" attribute.
Too bad we can't get a sneak peek at the new manuals... reviewing some
of the code anyway.
>
> Signed-off-by: Liang Gao <gaoliang@...ngson.cn>
> Signed-off-by: Jun Yi <yijun@...ngson.cn>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
> arch/loongarch/include/asm/cpu-features.h | 2 +-
> arch/loongarch/include/asm/cpu.h | 2 ++
> arch/loongarch/include/asm/loongarch.h | 4 ++++
> arch/loongarch/include/asm/pgtable.h | 4 ++--
> arch/loongarch/include/asm/tlb.h | 3 +++
> arch/loongarch/include/uapi/asm/hwcap.h | 1 +
> arch/loongarch/kernel/cpu-probe.c | 4 ++++
> arch/loongarch/kernel/proc.c | 1 +
> arch/loongarch/mm/tlb.c | 24 ++++++++++++++++++-----
> arch/loongarch/mm/tlbex.S | 21 ++++++++++++++++++++
> 10 files changed, 58 insertions(+), 8 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/cpu-features.h b/arch/loongarch/include/asm/cpu-features.h
> index f6177f133477..2eafe6a6aca8 100644
> --- a/arch/loongarch/include/asm/cpu-features.h
> +++ b/arch/loongarch/include/asm/cpu-features.h
> @@ -64,6 +64,6 @@
> #define cpu_has_eiodecode cpu_opt(LOONGARCH_CPU_EIODECODE)
> #define cpu_has_guestid cpu_opt(LOONGARCH_CPU_GUESTID)
> #define cpu_has_hypervisor cpu_opt(LOONGARCH_CPU_HYPERVISOR)
> -
> +#define cpu_has_ptw cpu_opt(LOONGARCH_CPU_PTW)
>
> #endif /* __ASM_CPU_FEATURES_H */
> diff --git a/arch/loongarch/include/asm/cpu.h b/arch/loongarch/include/asm/cpu.h
> index 88773d849e33..48b9f7168bcc 100644
> --- a/arch/loongarch/include/asm/cpu.h
> +++ b/arch/loongarch/include/asm/cpu.h
> @@ -98,6 +98,7 @@ enum cpu_type_enum {
> #define CPU_FEATURE_EIODECODE 23 /* CPU has EXTIOI interrupt pin decode mode */
> #define CPU_FEATURE_GUESTID 24 /* CPU has GuestID feature */
> #define CPU_FEATURE_HYPERVISOR 25 /* CPU has hypervisor (running in VM) */
> +#define CPU_FEATURE_PTW 26 /* CPU has hardware page table walker */
>
> #define LOONGARCH_CPU_CPUCFG BIT_ULL(CPU_FEATURE_CPUCFG)
> #define LOONGARCH_CPU_LAM BIT_ULL(CPU_FEATURE_LAM)
> @@ -125,5 +126,6 @@ enum cpu_type_enum {
> #define LOONGARCH_CPU_EIODECODE BIT_ULL(CPU_FEATURE_EIODECODE)
> #define LOONGARCH_CPU_GUESTID BIT_ULL(CPU_FEATURE_GUESTID)
> #define LOONGARCH_CPU_HYPERVISOR BIT_ULL(CPU_FEATURE_HYPERVISOR)
> +#define LOONGARCH_CPU_PTW BIT_ULL(CPU_FEATURE_PTW)
>
> #endif /* _ASM_CPU_H */
> diff --git a/arch/loongarch/include/asm/loongarch.h b/arch/loongarch/include/asm/loongarch.h
> index b3323ab5b78d..93b22a7af654 100644
> --- a/arch/loongarch/include/asm/loongarch.h
> +++ b/arch/loongarch/include/asm/loongarch.h
> @@ -138,6 +138,7 @@ static inline u32 read_cpucfg(u32 reg)
> #define CPUCFG2_MIPSBT BIT(20)
> #define CPUCFG2_LSPW BIT(21)
> #define CPUCFG2_LAM BIT(22)
> +#define CPUCFG2_PTW BIT(24)
>
> #define LOONGARCH_CPUCFG3 0x3
> #define CPUCFG3_CCDMA BIT(0)
> @@ -453,6 +454,9 @@ static __always_inline void iocsr_write64(u64 val, u32 reg)
> #define CSR_PWCTL0_PTBASE (_ULCAST_(0x1f) << CSR_PWCTL0_PTBASE_SHIFT)
>
> #define LOONGARCH_CSR_PWCTL1 0x1d /* PWCtl1 */
> +#define CSR_PWCTL1_PTW_SHIFT 24
> +#define CSR_PWCTL1_PTW_WIDTH 1
> +#define CSR_PWCTL1_PTW (_ULCAST_(0x1) << CSR_PWCTL1_PTW_SHIFT)
> #define CSR_PWCTL1_DIR3WIDTH_SHIFT 18
> #define CSR_PWCTL1_DIR3WIDTH_WIDTH 5
> #define CSR_PWCTL1_DIR3WIDTH (_ULCAST_(0x1f) << CSR_PWCTL1_DIR3WIDTH_SHIFT)
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index d28fb9dbec59..5f93d6eef657 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -362,7 +362,7 @@ extern pgd_t invalid_pg_dir[];
> */
> static inline int pte_write(pte_t pte) { return pte_val(pte) & _PAGE_WRITE; }
> static inline int pte_young(pte_t pte) { return pte_val(pte) & _PAGE_ACCESSED; }
> -static inline int pte_dirty(pte_t pte) { return pte_val(pte) & _PAGE_MODIFIED; }
> +static inline int pte_dirty(pte_t pte) { return pte_val(pte) & (_PAGE_DIRTY | _PAGE_MODIFIED); }
Will this affect existing models? I can't seem to remember the details.
>
> static inline pte_t pte_mkold(pte_t pte)
> {
> @@ -506,7 +506,7 @@ static inline pmd_t pmd_wrprotect(pmd_t pmd)
>
> static inline int pmd_dirty(pmd_t pmd)
> {
> - return !!(pmd_val(pmd) & _PAGE_MODIFIED);
> + return !!(pmd_val(pmd) & (_PAGE_DIRTY | _PAGE_MODIFIED));
> }
>
> static inline pmd_t pmd_mkclean(pmd_t pmd)
> diff --git a/arch/loongarch/include/asm/tlb.h b/arch/loongarch/include/asm/tlb.h
> index f5e4deb97402..0dc9ee2b05d2 100644
> --- a/arch/loongarch/include/asm/tlb.h
> +++ b/arch/loongarch/include/asm/tlb.h
> @@ -163,6 +163,9 @@ extern void handle_tlb_store(void);
> extern void handle_tlb_modify(void);
> extern void handle_tlb_refill(void);
> extern void handle_tlb_protect(void);
> +extern void handle_tlb_load_ptw(void);
> +extern void handle_tlb_store_ptw(void);
> +extern void handle_tlb_modify_ptw(void);
>
> extern void dump_tlb_all(void);
> extern void dump_tlb_regs(void);
> diff --git a/arch/loongarch/include/uapi/asm/hwcap.h b/arch/loongarch/include/uapi/asm/hwcap.h
> index 8840b72fa8e8..6955a7cb2c65 100644
> --- a/arch/loongarch/include/uapi/asm/hwcap.h
> +++ b/arch/loongarch/include/uapi/asm/hwcap.h
> @@ -16,5 +16,6 @@
> #define HWCAP_LOONGARCH_LBT_X86 (1 << 10)
> #define HWCAP_LOONGARCH_LBT_ARM (1 << 11)
> #define HWCAP_LOONGARCH_LBT_MIPS (1 << 12)
> +#define HWCAP_LOONGARCH_PTW (1 << 13)
This feature should be irrevelant to userspace, right? We should
probably not add it here.
>
> #endif /* _UAPI_ASM_HWCAP_H */
> diff --git a/arch/loongarch/kernel/cpu-probe.c b/arch/loongarch/kernel/cpu-probe.c
> index f42acc6c8df6..e925579c7a71 100644
> --- a/arch/loongarch/kernel/cpu-probe.c
> +++ b/arch/loongarch/kernel/cpu-probe.c
> @@ -136,6 +136,10 @@ static void cpu_probe_common(struct cpuinfo_loongarch *c)
> c->options |= LOONGARCH_CPU_CRYPTO;
> elf_hwcap |= HWCAP_LOONGARCH_CRYPTO;
> }
> + if (config & CPUCFG2_PTW) {
> + c->options |= LOONGARCH_CPU_PTW;
> + elf_hwcap |= HWCAP_LOONGARCH_PTW;
> + }
> if (config & CPUCFG2_LVZP) {
> c->options |= LOONGARCH_CPU_LVZ;
> elf_hwcap |= HWCAP_LOONGARCH_LVZ;
> diff --git a/arch/loongarch/kernel/proc.c b/arch/loongarch/kernel/proc.c
> index 0d82907b5404..782a34e7336e 100644
> --- a/arch/loongarch/kernel/proc.c
> +++ b/arch/loongarch/kernel/proc.c
> @@ -79,6 +79,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> if (cpu_has_crc32) seq_printf(m, " crc32");
> if (cpu_has_complex) seq_printf(m, " complex");
> if (cpu_has_crypto) seq_printf(m, " crypto");
> + if (cpu_has_ptw) seq_printf(m, " ptw");
> if (cpu_has_lvz) seq_printf(m, " lvz");
> if (cpu_has_lbt_x86) seq_printf(m, " lbt_x86");
> if (cpu_has_lbt_arm) seq_printf(m, " lbt_arm");
> diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
> index 8bad6b0cff59..3e1d1d3c7058 100644
> --- a/arch/loongarch/mm/tlb.c
> +++ b/arch/loongarch/mm/tlb.c
> @@ -167,6 +167,9 @@ void __update_tlb(struct vm_area_struct *vma, unsigned long address, pte_t *ptep
> int idx;
> unsigned long flags;
>
> + if (cpu_has_ptw)
> + return;
> +
> /*
> * Handle debugger faulting in for debugee.
> */
> @@ -220,7 +223,11 @@ static void setup_ptwalker(void)
> pte_w = PAGE_SHIFT - 3;
>
> pwctl0 = pte_i | pte_w << 5 | pmd_i << 10 | pmd_w << 15 | pud_i << 20 | pud_w << 25;
> - pwctl1 = pgd_i | pgd_w << 6;
> +
> + if (!cpu_has_ptw)
> + pwctl1 = pgd_i | pgd_w << 6;
> + else
> + pwctl1 = pgd_i | pgd_w << 6 | CSR_PWCTL1_PTW;
This is better in avoiding the duplication:
if (cpu_has_ptw)
pwctl1 |= CSR_PWCTL1_PTW;
>
> csr_write64(pwctl0, LOONGARCH_CSR_PWCTL0);
> csr_write64(pwctl1, LOONGARCH_CSR_PWCTL1);
> @@ -264,10 +271,17 @@ void setup_tlb_handler(int cpu)
> if (cpu == 0) {
> memcpy((void *)tlbrentry, handle_tlb_refill, 0x80);
> local_flush_icache_range(tlbrentry, tlbrentry + 0x80);
> - set_handler(EXCCODE_TLBI * VECSIZE, handle_tlb_load, VECSIZE);
> - set_handler(EXCCODE_TLBL * VECSIZE, handle_tlb_load, VECSIZE);
> - set_handler(EXCCODE_TLBS * VECSIZE, handle_tlb_store, VECSIZE);
> - set_handler(EXCCODE_TLBM * VECSIZE, handle_tlb_modify, VECSIZE);
> + if (!cpu_has_ptw) {
Better not have the condition inverted for less cognitive burden (have
to go "no [hardware] page table walker" -> "take the software approach"
otherwise).
> + set_handler(EXCCODE_TLBI * VECSIZE, handle_tlb_load, VECSIZE);
> + set_handler(EXCCODE_TLBL * VECSIZE, handle_tlb_load, VECSIZE);
> + set_handler(EXCCODE_TLBS * VECSIZE, handle_tlb_store, VECSIZE);
> + set_handler(EXCCODE_TLBM * VECSIZE, handle_tlb_modify, VECSIZE);
> + } else {
> + set_handler(EXCCODE_TLBI * VECSIZE, handle_tlb_load_ptw, VECSIZE);
> + set_handler(EXCCODE_TLBL * VECSIZE, handle_tlb_load_ptw, VECSIZE);
> + set_handler(EXCCODE_TLBS * VECSIZE, handle_tlb_store_ptw, VECSIZE);
> + set_handler(EXCCODE_TLBM * VECSIZE, handle_tlb_modify_ptw, VECSIZE);
> + }
> set_handler(EXCCODE_TLBNR * VECSIZE, handle_tlb_protect, VECSIZE);
> set_handler(EXCCODE_TLBNX * VECSIZE, handle_tlb_protect, VECSIZE);
> set_handler(EXCCODE_TLBPE * VECSIZE, handle_tlb_protect, VECSIZE);
> diff --git a/arch/loongarch/mm/tlbex.S b/arch/loongarch/mm/tlbex.S
> index 240ced55586e..01df8a0b87f6 100644
> --- a/arch/loongarch/mm/tlbex.S
> +++ b/arch/loongarch/mm/tlbex.S
> @@ -190,6 +190,13 @@ nopage_tlb_load:
> jr t0
> SYM_FUNC_END(handle_tlb_load)
>
> +SYM_FUNC_START(handle_tlb_load_ptw)
> + csrwr t0, LOONGARCH_CSR_KS0
> + csrwr t1, LOONGARCH_CSR_KS1
> + la_abs t0, tlb_do_page_fault_0
> + jirl zero, t0, 0
jr t0
> +SYM_FUNC_END(handle_tlb_load_ptw)
> +
> SYM_FUNC_START(handle_tlb_store)
> csrwr t0, EXCEPTION_KS0
> csrwr t1, EXCEPTION_KS1
> @@ -339,6 +346,13 @@ nopage_tlb_store:
> jr t0
> SYM_FUNC_END(handle_tlb_store)
>
> +SYM_FUNC_START(handle_tlb_store_ptw)
> + csrwr t0, LOONGARCH_CSR_KS0
> + csrwr t1, LOONGARCH_CSR_KS1
> + la_abs t0, tlb_do_page_fault_1
> + jirl zero, t0, 0
Same here.
> +SYM_FUNC_END(handle_tlb_store_ptw)
> +
> SYM_FUNC_START(handle_tlb_modify)
> csrwr t0, EXCEPTION_KS0
> csrwr t1, EXCEPTION_KS1
> @@ -486,6 +500,13 @@ nopage_tlb_modify:
> jr t0
> SYM_FUNC_END(handle_tlb_modify)
>
> +SYM_FUNC_START(handle_tlb_modify_ptw)
> + csrwr t0, LOONGARCH_CSR_KS0
> + csrwr t1, LOONGARCH_CSR_KS1
> + la_abs t0, tlb_do_page_fault_1
> + jirl zero, t0, 0
And here.
> +SYM_FUNC_END(handle_tlb_modify_ptw)
> +
> SYM_FUNC_START(handle_tlb_refill)
> csrwr t0, LOONGARCH_CSR_TLBRSAVE
> csrrd t0, LOONGARCH_CSR_PGD
--
WANG "xen0n" Xuerui
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