linux-kernel - Re: [PATCH v2] x86: enable RCU based table free

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Date:   Thu, 24 Aug 2017 18:06:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jork Loeser <Jork.Loeser@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v2] x86: enable RCU based table free

On Thu, Aug 24, 2017 at 05:27:21PM +0200, Vitaly Kuznetsov wrote:
> Do you think adding something like
> 
> /*
>  * While x86 architecture in general requires an IPI to perform TLB
>  * shootdown, enablement code for several hypervisors overrides
>  * .flush_tlb_others hook in pv_mmu_ops and implements it by issuing
>  * a hypercall. To keep software pagetable walkers safe in this case we 
>  * switch to RCU based table free (HAVE_RCU_TABLE_FREE). See the comment
>  * below 'ifdef CONFIG_HAVE_RCU_TABLE_FREE' in include/asm-generic/tlb.h
>  * for more details.
>  */
> 
> before __tlb_remove_table would suffice? Or do you see a better place
> for such comment?

Yes, that seems fine. Thanks!