linux-kernel - Re: [PATCH 04/10] x86,mm: use INVLPGB for kernel TLB flushes

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: <20241222111606.GU11133@noisy.programming.kicks-ass.net>
Date: Sun, 22 Dec 2024 12:16:06 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	dave.hansen@...ux.intel.com, luto@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, hpa@...or.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 04/10] x86,mm: use INVLPGB for kernel TLB flushes

On Sat, Dec 21, 2024 at 11:06:36PM -0500, Rik van Riel wrote:
> Use broadcast TLB invalidation for kernel addresses when available.
> 
> This stops us from having to send IPIs for kernel TLB flushes.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  arch/x86/mm/tlb.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 6cf881a942bb..09980fb17907 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -1077,6 +1077,33 @@ void flush_tlb_all(void)
>  	on_each_cpu(do_flush_tlb_all, NULL, 1);
>  }
>  
> +static void broadcast_kernel_range_flush(unsigned long start, unsigned long end)
> +{
> +	unsigned long addr;
> +	unsigned long maxnr = boot_cpu_data.invlpgb_count_max;
> +	unsigned long threshold = tlb_single_page_flush_ceiling * maxnr;
> +
> +	/*
> +	 * TLBSYNC only waits for flushes originating on the same CPU.
> +	 * Disabling migration allows us to wait on all flushes.
> +	 */
> +	migrate_disable();

So how expensive is all this? That is, I think I would feel better is
this were preempt_disable().

> +
> +	if (end == TLB_FLUSH_ALL ||
> +	    (end - start) > threshold << PAGE_SHIFT) {
> +		invlpgb_flush_all();
> +	} else {
> +		unsigned long nr;
> +		for (addr = start; addr < end; addr += nr << PAGE_SHIFT) {
> +			nr = min((end - addr) >> PAGE_SHIFT, maxnr);
> +			invlpgb_flush_addr(addr, nr);
> +		}
> +	}
> +
> +	tlbsync();
> +	migrate_enable();
> +}
> +
>  static void do_kernel_range_flush(void *info)
>  {
>  	struct flush_tlb_info *f = info;
> @@ -1089,6 +1116,11 @@ static void do_kernel_range_flush(void *info)
>  
>  void flush_tlb_kernel_range(unsigned long start, unsigned long end)
>  {
> +	if (static_cpu_has(X86_FEATURE_INVLPGB)) {
> +		broadcast_kernel_range_flush(start, end);
> +		return;
> +	}
> +
>  	/* Balance as user space task's flush, a bit conservative */
>  	if (end == TLB_FLUSH_ALL ||
>  	    (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
> -- 
> 2.47.1
>