| Message ID | 20240814081126.956287-3-samuel.holland@sifive.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | riscv: Per-thread envcfg CSR support | expand |
On Wed, Aug 14, 2024 at 01:10:55AM -0700, Samuel Holland wrote: > Some bits in the [ms]envcfg CSR, such as the CFI state and pointer > masking mode, need to be controlled on a per-thread basis. Support this > by keeping a copy of the CSR value in struct thread_struct and writing > it during context switches. It is safe to discard the old CSR value > during the context switch because the CSR is modified only by software, > so the CSR will remain in sync with the copy in thread_struct. > > Use ALTERNATIVE directly instead of riscv_has_extension_unlikely() to > minimize branchiness in the context switching code. > > Since thread_struct is copied during fork(), setting the value for the > init task sets the default value for all other threads. > > Reviewed-by: Andrew Jones <ajones@ventanamicro.com> > Reviewed-by: Deepak Gupta <debug@rivosinc.com> > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> > --- Reviewed-by: Charlie Jenkins <charlie@rivosinc.com> > > (no changes since v1) > > arch/riscv/include/asm/processor.h | 1 + > arch/riscv/include/asm/switch_to.h | 8 ++++++++ > arch/riscv/kernel/cpufeature.c | 2 +- > 3 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h > index 8702b8721a27..586e4ab701c4 100644 > --- a/arch/riscv/include/asm/processor.h > +++ b/arch/riscv/include/asm/processor.h > @@ -124,6 +124,7 @@ struct thread_struct { > unsigned long s[12]; /* s[0]: frame pointer */ > struct __riscv_d_ext_state fstate; > unsigned long bad_cause; > + unsigned long envcfg; > u32 riscv_v_flags; > u32 vstate_ctrl; > struct __riscv_v_ext_state vstate; > diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h > index 7594df37cc9f..9685cd85e57c 100644 > --- a/arch/riscv/include/asm/switch_to.h > +++ b/arch/riscv/include/asm/switch_to.h > @@ -70,6 +70,13 @@ static __always_inline bool has_fpu(void) { return false; } > #define __switch_to_fpu(__prev, __next) do { } while (0) > #endif > > +static inline void __switch_to_envcfg(struct task_struct *next) > +{ > + asm volatile (ALTERNATIVE("nop", "csrw " __stringify(CSR_ENVCFG) ", %0", > + 0, RISCV_ISA_EXT_XLINUXENVCFG, 1) > + :: "r" (next->thread.envcfg) : "memory"); > +} > + > extern struct task_struct *__switch_to(struct task_struct *, > struct task_struct *); > > @@ -103,6 +110,7 @@ do { \ > __switch_to_vector(__prev, __next); \ > if (switch_to_should_flush_icache(__next)) \ > local_flush_icache_all(); \ > + __switch_to_envcfg(__next); \ > ((last) = __switch_to(__prev, __next)); \ > } while (0) > > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c > index 0139d4ea8426..df3e7e8d6d78 100644 > --- a/arch/riscv/kernel/cpufeature.c > +++ b/arch/riscv/kernel/cpufeature.c > @@ -922,7 +922,7 @@ unsigned long riscv_get_elf_hwcap(void) > void riscv_user_isa_enable(void) > { > if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICBOZ)) > - csr_set(CSR_ENVCFG, ENVCFG_CBZE); > + current->thread.envcfg |= ENVCFG_CBZE; > else if (any_cpu_has_zicboz) > pr_warn_once("Zicboz disabled as it is unavailable on some harts\n"); > } > -- > 2.45.1 >
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index 8702b8721a27..586e4ab701c4 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -124,6 +124,7 @@ struct thread_struct { unsigned long s[12]; /* s[0]: frame pointer */ struct __riscv_d_ext_state fstate; unsigned long bad_cause; + unsigned long envcfg; u32 riscv_v_flags; u32 vstate_ctrl; struct __riscv_v_ext_state vstate; diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h index 7594df37cc9f..9685cd85e57c 100644 --- a/arch/riscv/include/asm/switch_to.h +++ b/arch/riscv/include/asm/switch_to.h @@ -70,6 +70,13 @@ static __always_inline bool has_fpu(void) { return false; } #define __switch_to_fpu(__prev, __next) do { } while (0) #endif +static inline void __switch_to_envcfg(struct task_struct *next) +{ + asm volatile (ALTERNATIVE("nop", "csrw " __stringify(CSR_ENVCFG) ", %0", + 0, RISCV_ISA_EXT_XLINUXENVCFG, 1) + :: "r" (next->thread.envcfg) : "memory"); +} + extern struct task_struct *__switch_to(struct task_struct *, struct task_struct *); @@ -103,6 +110,7 @@ do { \ __switch_to_vector(__prev, __next); \ if (switch_to_should_flush_icache(__next)) \ local_flush_icache_all(); \ + __switch_to_envcfg(__next); \ ((last) = __switch_to(__prev, __next)); \ } while (0) diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 0139d4ea8426..df3e7e8d6d78 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -922,7 +922,7 @@ unsigned long riscv_get_elf_hwcap(void) void riscv_user_isa_enable(void) { if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICBOZ)) - csr_set(CSR_ENVCFG, ENVCFG_CBZE); + current->thread.envcfg |= ENVCFG_CBZE; else if (any_cpu_has_zicboz) pr_warn_once("Zicboz disabled as it is unavailable on some harts\n"); }