linux-kernel - Re: [PATCH v13 05/14] x86/mm: use INVLPGB in flush_tlb

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Message-ID: <20250224124612.GGZ7xqFMYXmoRXqKdP@fat_crate.local>
Date: Mon, 24 Feb 2025 13:46:12 +0100
From: Borislav Petkov <bp@...en8.de>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, peterz@...radead.org,
	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, jackmanb@...gle.com,
	jannh@...gle.com, mhklinux@...look.com, andrew.cooper3@...rix.com,
	Manali.Shukla@....com, mingo@...nel.org
Subject: Re: [PATCH v13 05/14] x86/mm: use INVLPGB in flush_tlb_all

On Sun, Feb 23, 2025 at 02:48:55PM -0500, Rik van Riel wrote:
> The flush_tlb_all() function is not used a whole lot, but we might
> as well use broadcast TLB flushing there, too.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> Tested-by: Manali Shukla <Manali.Shukla@....com>
> Tested-by: Brendan Jackman <jackmanb@...gle.com>
> Tested-by: Michael Kelley <mhklinux@...look.com>
> ---
>  arch/x86/mm/tlb.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 59396a3c6e9c..2d7ed0fda61f 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -1065,6 +1065,16 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
>  }
>  
>  
> +static bool broadcast_flush_tlb_all(void)

broadcast?

All those INVLPGB functions have a "invlpgb_" prefix...

In any case, get rid of that function:

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 2d7ed0fda61f..feaca53b7685 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1065,16 +1065,6 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 }
 
 
-static bool broadcast_flush_tlb_all(void)
-{
-	if (!cpu_feature_enabled(X86_FEATURE_INVLPGB))
-		return false;
-
-	guard(preempt)();
-	invlpgb_flush_all();
-	return true;
-}
-
 static void do_flush_tlb_all(void *info)
 {
 	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
@@ -1085,9 +1075,11 @@ void flush_tlb_all(void)
 {
 	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
 
-	/* First try (faster) hardware-assisted TLB invalidation. */
-	if (broadcast_flush_tlb_all())
+	if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
+		guard(preempt)();
+		invlpgb_flush_all();
 		return;
+	}
 
 	/* Fall back to the IPI-based invalidation. */
 	on_each_cpu(do_flush_tlb_all, NULL, 1);

-- 
Regards/Gruss,
    Boris.

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