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| author |   Jason A. Donenfeld <Jason@zx2c4.com> | 2024-09-06 21:06:55 +0200 |
|---|---|---|
| committer | Jason A. Donenfeld <Jason@zx2c4.com> | 2024-11-18 03:15:17 +0100 |
| commit | 02c7dbd2f56e02a4ca3910fc91b574ed4897a19e (patch) | |
| tree | 0a333c2d1535d950d108cc42ceae8908f4b0fa78 | |
| parent | firmware_loader: always print path of firmware (diff) | |
| download | laptop-kernel-master.tar.xz laptop-kernel-master.zip | |
The expression `((void *)&__timens_vdso_data - (void *)&__vdso_data)`
seems harmless, but it actually results in quite a bit of code and two
jumps, in a place that's supposed to be somewhat lean on code. The value
of that calculation is always 3*PAGE_SIZE, as it turns out. Changing it
to that results in a more modest cmov instruction being emitted. It also
makes it a bit more clear what's happening.
To accomplish this, define offset macros in vvar.h, which can be shared
by C code and by the linker script that decides where these pages will
actually go.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
| -rw-r--r-- | arch/x86/entry/vdso/vdso-layout.lds.S | 11 | ||||
| -rw-r--r-- | arch/x86/include/asm/vdso/getrandom.h | 2 | ||||
| -rw-r--r-- | arch/x86/include/asm/vvar.h | 5 |
3 files changed, 11 insertions, 7 deletions
diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S index bafa73f09e92..ddd6999b6946 100644 --- a/arch/x86/entry/vdso/vdso-layout.lds.S +++ b/arch/x86/entry/vdso/vdso-layout.lds.S @@ -16,17 +16,16 @@ SECTIONS * segment. */ - vvar_start = . - 4 * PAGE_SIZE; - vvar_page = vvar_start; - /* Place all vvars at the offsets in asm/vvar.h. */ #define EMIT_VVAR(name, offset) vvar_ ## name = vvar_page + offset; #include <asm/vvar.h> #undef EMIT_VVAR - pvclock_page = vvar_start + PAGE_SIZE; - hvclock_page = vvar_start + 2 * PAGE_SIZE; - timens_page = vvar_start + 3 * PAGE_SIZE; + vvar_start = . - 4 * PAGE_SIZE; + vvar_page = vvar_start + VVAR_PAGE_OFFSET * PAGE_SIZE; + pvclock_page = vvar_start + PVCLOCK_PAGE_OFFSET * PAGE_SIZE; + hvclock_page = vvar_start + HVCLOCK_PAGE_OFFSET * PAGE_SIZE; + timens_page = vvar_start + TIMENS_PAGE_OFFSET * PAGE_SIZE; #undef _ASM_X86_VVAR_H /* Place all vvars in timens too at the offsets in asm/vvar.h. */ diff --git a/arch/x86/include/asm/vdso/getrandom.h b/arch/x86/include/asm/vdso/getrandom.h index ff5334ad32a0..f14ff0dcbb1e 100644 --- a/arch/x86/include/asm/vdso/getrandom.h +++ b/arch/x86/include/asm/vdso/getrandom.h @@ -33,7 +33,7 @@ static __always_inline ssize_t getrandom_syscall(void *buffer, size_t len, unsig static __always_inline const struct vdso_rng_data *__arch_get_vdso_rng_data(void) { if (IS_ENABLED(CONFIG_TIME_NS) && __vdso_data->clock_mode == VDSO_CLOCKMODE_TIMENS) - return (void *)&__vdso_rng_data + ((void *)&__timens_vdso_data - (void *)&__vdso_data); + return (void *)&__vdso_rng_data + (TIMENS_PAGE_OFFSET << CONFIG_PAGE_SHIFT); return &__vdso_rng_data; } diff --git a/arch/x86/include/asm/vvar.h b/arch/x86/include/asm/vvar.h index 9d9af37f7cab..d2a2ffa72909 100644 --- a/arch/x86/include/asm/vvar.h +++ b/arch/x86/include/asm/vvar.h @@ -19,6 +19,11 @@ #ifndef _ASM_X86_VVAR_H #define _ASM_X86_VVAR_H +#define VVAR_PAGE_OFFSET 0 +#define PVCLOCK_PAGE_OFFSET 1 +#define HVCLOCK_PAGE_OFFSET 2 +#define TIMENS_PAGE_OFFSET 3 + #ifdef EMIT_VVAR /* * EMIT_VVAR() is used by the kernel linker script to put vvars in the |