RE: [PATCH v4 05/12] x86/mm: add INVLPGB support code

[Michael Kelley <mhklinux@outlook.com>]

From: riel@surriel.com <riel@surriel.com> Sent: Sunday, January 12, 2025 7:54 AM
> 
> Add invlpgb.h with the helper functions and definitions needed to use
> broadcast TLB invalidation on AMD EPYC 3 and newer CPUs.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
>  arch/x86/include/asm/invlpgb.h  | 95 +++++++++++++++++++++++++++++++++
>  arch/x86/include/asm/tlbflush.h |  1 +
>  2 files changed, 96 insertions(+)
>  create mode 100644 arch/x86/include/asm/invlpgb.h
> 
> diff --git a/arch/x86/include/asm/invlpgb.h b/arch/x86/include/asm/invlpgb.h
> new file mode 100644
> index 000000000000..d62e3733a1ab
> --- /dev/null
> +++ b/arch/x86/include/asm/invlpgb.h
> @@ -0,0 +1,95 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_X86_INVLPGB
> +#define _ASM_X86_INVLPGB
> +
> +#include <vdso/bits.h>
> +
> +/*
> + * INVLPGB does broadcast TLB invalidation across all the CPUs in the system.
> + *
> + * The INVLPGB instruction is weakly ordered, and a batch of invalidations can
> + * be done in a parallel fashion.
> + *
> + * TLBSYNC is used to ensure that pending INVLPGB invalidations initiated from
> + * this CPU have completed.
> + */
> +static inline void __invlpgb(unsigned long asid, unsigned long pcid, unsigned long addr,
> +			    int extra_count, bool pmd_stride, unsigned long flags)
> +{
> +	u32 edx = (pcid << 16) | asid;
> +	u32 ecx = (pmd_stride << 31);
> +	u64 rax = addr | flags;
> +
> +	/* Protect against negative numbers. */
> +	extra_count = max(extra_count, 0);
> +	ecx |= extra_count;
> +
> +	asm volatile("invlpgb" : : "a" (rax), "c" (ecx), "d" (edx));

The above needs to be:

	asm volatile(".byte 0x0f, 0x01, 0xfe" : : "a" (rax), "c" (ecx), "d" (edx));

plus an explanatory comment.

As Boris Petkov previously noted[1], the "invlpgb" instruction name requires
binutils version 2.36. But the current Linux kernel minimum binutils version
is 2.25 (in scripts/min-tool-version.sh). For example, I'm using binutils 2.34,
and your asm statement doesn't compile.

> +}
> +
> +/* Wait for INVLPGB originated by this CPU to complete. */
> +static inline void tlbsync(void)
> +{
> +	asm volatile("tlbsync");

Same as above for "tlbsync".

Michael

[1] https://lore.kernel.org/lkml/20250102124247.GPZ3aJx8JTJa6PcaOW@fat_crate.local/