linux-kernel - Re: [PATCH v6 05/12] x86/mm: add INVLPGB support code

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Message-ID: <20250121094540.GA5388@noisy.programming.kicks-ass.net>
Date: Tue, 21 Jan 2025 10:45:40 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, bp@...en8.de,
	dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
	nadav.amit@...il.com, thomas.lendacky@....com, kernel-team@...a.com,
	linux-mm@...ck.org, akpm@...ux-foundation.org, jannh@...gle.com,
	mhklinux@...look.com, andrew.cooper3@...rix.com
Subject: Re: [PATCH v6 05/12] x86/mm: add INVLPGB support code

On Sun, Jan 19, 2025 at 09:40:13PM -0500, Rik van Riel wrote:

> +/*
> + * 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, u16 extra_count,
> +			     bool pmd_stride, unsigned long flags)
> +{
> +	u32 edx = (pcid << 16) | asid;
> +	u32 ecx = (pmd_stride << 31) | extra_count;
> +	u64 rax = addr | flags;
> +
> +	/* INVLPGB; supported in binutils >= 2.36. */
> +	asm volatile(".byte 0x0f, 0x01, 0xfe" : : "a" (rax), "c" (ecx), "d" (edx));
> +}

So asid is always 0 (for now), but I'd feel better if that was a u16
argument, less chance funnies when someone starts using it.

We should probably mask or WARN on addr having low bits set, and flags
should then be a u8 or something.