unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
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riscv: vector: adjust minimum Vector requirement to ZVE32X

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Make has_vector() to check for ZVE32X. Every in-kernel usage of V that
requires a more complicate version of V must then call out explicitly.

Also, change riscv_v_first_use_handler(), and boot code that calls
riscv_v_setup_vsize() to accept ZVE32X.

Most kernel/user interfaces requires minimum of ZVE32X. Thus, programs
compiled and run with ZVE32X should be supported by the kernel on most
aspects. This includes context-switch, signal, ptrace, prctl, and
hwprobe.

One exception is that ELF_HWCAP returns 'V' only if full V is supported
on the platform. This means that the system without a full V must not
rely on ELF_HWCAP to tell whether it is allowable to execute Vector
without first invoking a prctl() check.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Acked-by: Joel Granados <j.granados@samsung.com>
Link: https://lore.kernel.org/r/20240510-zve-detection-v5-7-0711bdd26c12@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Andy Chiu 2024-05-10 00:26:57 +08:00 committed by Palmer Dabbelt
parent de8f8282a9
commit ac295b6742
No known key found for this signature in database
GPG key ID: 2E1319F35FBB1889
5 changed files with 19 additions and 9 deletions
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10
arch/riscv/include/asm/vector.h
View file

@ -37,7 +37,7 @@ static inline u32 riscv_v_flags(void)
static __always_inline bool has_vector(void)
{
return riscv_has_extension_unlikely(RISCV_ISA_EXT_v);
return riscv_has_extension_unlikely(RISCV_ISA_EXT_ZVE32X);
}
static inline void __riscv_v_vstate_clean(struct pt_regs *regs)
@ -91,7 +91,7 @@ static __always_inline void __vstate_csr_restore(struct __riscv_v_ext_state *src
{
asm volatile (
".option push\n\t"
".option arch, +v\n\t"
".option arch, +zve32x\n\t"
"vsetvl x0, %2, %1\n\t"
".option pop\n\t"
"csrw " __stringify(CSR_VSTART) ", %0\n\t"
@ -109,7 +109,7 @@ static inline void __riscv_v_vstate_save(struct __riscv_v_ext_state *save_to,
__vstate_csr_save(save_to);
asm volatile (
".option push\n\t"
".option arch, +v\n\t"
".option arch, +zve32x\n\t"
"vsetvli %0, x0, e8, m8, ta, ma\n\t"
"vse8.v v0, (%1)\n\t"
"add %1, %1, %0\n\t"
@ -131,7 +131,7 @@ static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_
riscv_v_enable();
asm volatile (
".option push\n\t"
".option arch, +v\n\t"
".option arch, +zve32x\n\t"
"vsetvli %0, x0, e8, m8, ta, ma\n\t"
"vle8.v v0, (%1)\n\t"
"add %1, %1, %0\n\t"
@ -153,7 +153,7 @@ static inline void __riscv_v_vstate_discard(void)
riscv_v_enable();
asm volatile (
".option push\n\t"
".option arch, +v\n\t"
".option arch, +zve32x\n\t"
"vsetvli %0, x0, e8, m8, ta, ma\n\t"
"vmv.v.i v0, -1\n\t"
"vmv.v.i v8, -1\n\t"

5
arch/riscv/kernel/cpufeature.c
View file

@ -724,11 +724,14 @@ void __init riscv_fill_hwcap(void)
elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
}
if (elf_hwcap & COMPAT_HWCAP_ISA_V) {
if (__riscv_isa_extension_available(NULL, RISCV_ISA_EXT_ZVE32X)) {
/*
* This cannot fail when called on the boot hart
*/
riscv_v_setup_vsize();
}
if (elf_hwcap & COMPAT_HWCAP_ISA_V) {
/*
* ISA string in device tree might have 'v' flag, but
* CONFIG_RISCV_ISA_V is disabled in kernel.

6
arch/riscv/kernel/sys_hwprobe.c
View file

@ -69,7 +69,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
if (riscv_isa_extension_available(NULL, c))
pair->value |= RISCV_HWPROBE_IMA_C;
if (has_vector())
if (has_vector() && riscv_isa_extension_available(NULL, v))
pair->value |= RISCV_HWPROBE_IMA_V;
/*
@ -113,6 +113,10 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
EXT_KEY(ZICOND);
EXT_KEY(ZIHINTPAUSE);
/*
* All the following extensions must depend on the kernel
* support of V.
*/
if (has_vector()) {
EXT_KEY(ZVE32X);
EXT_KEY(ZVE32F);

5
arch/riscv/kernel/vector.c
View file

@ -173,8 +173,11 @@ bool riscv_v_first_use_handler(struct pt_regs *regs)
u32 __user *epc = (u32 __user *)regs->epc;
u32 insn = (u32)regs->badaddr;
if (!has_vector())
return false;
/* Do not handle if V is not supported, or disabled */
if (!(ELF_HWCAP & COMPAT_HWCAP_ISA_V))
if (!riscv_v_vstate_ctrl_user_allowed())
return false;
/* If V has been enabled then it is not the first-use trap */

2
arch/riscv/lib/uaccess.S
View file

@ -14,7 +14,7 @@
SYM_FUNC_START(__asm_copy_to_user)
#ifdef CONFIG_RISCV_ISA_V
ALTERNATIVE("j fallback_scalar_usercopy", "nop", 0, RISCV_ISA_EXT_v, CONFIG_RISCV_ISA_V)
ALTERNATIVE("j fallback_scalar_usercopy", "nop", 0, RISCV_ISA_EXT_ZVE32X, CONFIG_RISCV_ISA_V)
REG_L t0, riscv_v_usercopy_threshold
bltu a2, t0, fallback_scalar_usercopy
tail enter_vector_usercopy