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

[Kirill A. Shutemov]

On Thu, Jun 19, 2025 at 04:03:58PM -0400, Rik van Riel wrote:
> From: Rik van Riel <riel@xxxxxx>
> 
> 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@xxxxxxxxxxx>
> ---
>  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