linux-kernel - Re: [RFC PATCH v4 6/8] x86/mm: use RAR for kernel TLB flushes

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Message-ID: <um6emftj5lmto2ivddovvxl7lz4uvwduuwq725a3n7qykepmtc@cq6y4yez2hcv>
Date: Fri, 27 Jun 2025 16:27:33 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com, 
	dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org, bp@...en8.de, 
	x86@...nel.org, nadav.amit@...il.com, seanjc@...gle.com, tglx@...utronix.de, 
	mingo@...nel.org, Rik van Riel <riel@...com>
Subject: Re: [RFC PATCH v4 6/8] x86/mm: use RAR for kernel TLB flushes

On Thu, Jun 19, 2025 at 04:03:58PM -0400, Rik van Riel wrote:
> From: Rik van Riel <riel@...com>
> 
> Use Intel RAR for kernel TLB flushes, when enabled.
> 
> Pass in PCID 0 to smp_call_rar_many() to flush the specified addresses,
> regardless of which PCID they might be cached under in any destination CPU.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  arch/x86/mm/tlb.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 39f80111e6f1..8931f7029d6c 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -21,6 +21,7 @@
>  #include <asm/apic.h>
>  #include <asm/msr.h>
>  #include <asm/perf_event.h>
> +#include <asm/rar.h>
>  #include <asm/tlb.h>
>  
>  #include "mm_internal.h"
> @@ -1468,6 +1469,18 @@ static void do_flush_tlb_all(void *info)
>  	__flush_tlb_all();
>  }
>  
> +static void rar_full_flush(const cpumask_t *cpumask)
> +{
> +	guard(preempt)();
> +	smp_call_rar_many(cpumask, 0, 0, TLB_FLUSH_ALL);
> +	invpcid_flush_all();

I don't follow why do we need to call invpcid_flush_all() here in addition
to smp_call_rar_many(). Hm?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov