6.9-stable review patch. If anyone has any objections, please let me know.
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From: Uros Bizjak ubizjak@gmail.com
[ Upstream commit 4e5b0e8003df05983b6dabcdde7ff447d53b49d7 ]
When building a 32-bit vDSO for a 64-bit kernel, games are played with CONFIG_X86_64. {this,raw}_cpu_read_8() macros are conditionally defined on CONFIG_X86_64 and when CONFIG_X86_64 is undefined in fake_32bit_build.h various build failures in generic percpu header files can happen. To make things worse, the build of 32-bit vDSO for a 64-bit kernel grew dependency on arch_raw_cpu_ptr() macro and the build fails if arch_raw_cpu_ptr() macro is not defined.
To mitigate these issues, x86 carefully defines arch_raw_cpu_ptr() to avoid any dependency on raw_cpu_read_8() and thus CONFIG_X86_64. W/o segment register support, the definition uses size-agnostic MOV asm mnemonic and hopes that _ptr argument won't ever be 64-bit size on 32-bit targets (although newer GCCs warn for this situation with "unsupported size for integer register"), and w/ segment register support the definition uses size-agnostic __raw_cpu_read() macro.
Fortunately, raw_cpu_read() is not used in 32-bit vDSO for a 64-bit kernel. However, we can't simply omit the definition of arch_raw_cpu_read(), since the build will fail when building vdso/vdso32/vclock_gettime.o.
The patch defines arch_raw_cpu_ptr to BUILD_BUG() when BUILD_VDSO32_64 macro is defined. This way, we are sure that arch_raw_cpu_ptr() won't actually be used in 32-bit VDSO for a 64-bit kernel, but it is still defined to prevent build failure.
Finally, we can unify arch_raw_cpu_ptr() between builds w/ and w/o x86 segment register support, substituting two tricky macro definitions with a straightforward implementation.
There is no size difference and no difference in number of this_cpu_off accesses between patched and unpatched kernel when the kernel is built either w/ and w/o segment register support.
Signed-off-by: Uros Bizjak ubizjak@gmail.com Signed-off-by: Ingo Molnar mingo@kernel.org Cc: Andy Lutomirski luto@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Link: https://lore.kernel.org/r/20240322102730.209141-1-ubizjak@gmail.com Stable-dep-of: a55c1fdad5f6 ("x86/percpu: Use __force to cast from __percpu address space") Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/percpu.h | 42 +++++++++++++++-------------------- 1 file changed, 18 insertions(+), 24 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h index b77bbb67e77b0..dbfde44d88a31 100644 --- a/arch/x86/include/asm/percpu.h +++ b/arch/x86/include/asm/percpu.h @@ -59,36 +59,30 @@ #define __force_percpu_prefix "%%"__stringify(__percpu_seg)":" #define __my_cpu_offset this_cpu_read(this_cpu_off)
-#ifdef CONFIG_USE_X86_SEG_SUPPORT -/* - * Efficient implementation for cases in which the compiler supports - * named address spaces. Allows the compiler to perform additional - * optimizations that can save more instructions. - */ -#define arch_raw_cpu_ptr(ptr) \ -({ \ - unsigned long tcp_ptr__; \ - tcp_ptr__ = __raw_cpu_read(, this_cpu_off); \ - \ - tcp_ptr__ += (__force unsigned long)(ptr); \ - (typeof(*(ptr)) __kernel __force *)tcp_ptr__; \ -}) -#else /* CONFIG_USE_X86_SEG_SUPPORT */ +#ifdef CONFIG_X86_64 +#define __raw_my_cpu_offset raw_cpu_read_8(this_cpu_off); +#else +#define __raw_my_cpu_offset raw_cpu_read_4(this_cpu_off); +#endif + /* * Compared to the generic __my_cpu_offset version, the following * saves one instruction and avoids clobbering a temp register. + * + * arch_raw_cpu_ptr should not be used in 32-bit VDSO for a 64-bit + * kernel, because games are played with CONFIG_X86_64 there and + * sizeof(this_cpu_off) becames 4. */ -#define arch_raw_cpu_ptr(ptr) \ +#ifndef BUILD_VDSO32_64 +#define arch_raw_cpu_ptr(_ptr) \ ({ \ - unsigned long tcp_ptr__; \ - asm ("mov " __percpu_arg(1) ", %0" \ - : "=r" (tcp_ptr__) \ - : "m" (__my_cpu_var(this_cpu_off))); \ - \ - tcp_ptr__ += (unsigned long)(ptr); \ - (typeof(*(ptr)) __kernel __force *)tcp_ptr__; \ + unsigned long tcp_ptr__ = __raw_my_cpu_offset; \ + tcp_ptr__ += (unsigned long)(_ptr); \ + (typeof(*(_ptr)) __kernel __force *)tcp_ptr__; \ }) -#endif /* CONFIG_USE_X86_SEG_SUPPORT */ +#else +#define arch_raw_cpu_ptr(_ptr) ({ BUILD_BUG(); (typeof(_ptr))0; }) +#endif
#define PER_CPU_VAR(var) %__percpu_seg:(var)__percpu_rel