linux-kernel - Re: [PATCH v13 06/14] x86/mm: use broadcast TLB flushing for page reclaim TLB flushing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250224132711.GHZ7xzr0vdhva3-TvK@fat_crate.local>
Date: Mon, 24 Feb 2025 14:27:11 +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 06/14] x86/mm: use broadcast TLB flushing for page
 reclaim TLB flushing

On Sun, Feb 23, 2025 at 02:48:56PM -0500, Rik van Riel wrote:
> In the page reclaim code, we only track the CPU(s) where the TLB needs
> to be flushed, rather than all the individual mappings that may be getting
> invalidated.
> 
> Use broadcast TLB flushing when that is available.
> 
> This is a temporary hack to ensure that the PCID context for
> tasks in the next patch gets properly flushed from the page

There's no "next patch" in git - just merge this three-liner with the next
one.

> reclaim code, because the IPI based flushing in arch_tlbbatch_flush
> only flushes the currently loaded TLB context on each CPU.
> 
> Patch 10 replaces this with the actual mechanism used to do

Same. No "patch 10" in git.

> broadcast TLB flushing from the page reclaim code.
> 
> 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 | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 2d7ed0fda61f..16839651f67f 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -1326,7 +1326,9 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
>  	 * a local TLB flush is needed. Optimize this use-case by calling
>  	 * flush_tlb_func_local() directly in this case.
>  	 */
> -	if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) {
> +	if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
> +		invlpgb_flush_all_nonglobals();

I'm confused. The docs say rAX needs to be 0x6 to do "Invalidate all TLB
entries that match {ASID, PCID} excluding Global". But you're calling INVLPGB
with rAX==0 and the APM doesn't say what this does.

I'm guessing you want this to mean invalidate all non-globals for any ASID and
PCID. So I muss be missing the place in the docs where it says so...

Hmmm?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette