linux-kernel - Re: [PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr by PUD

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Message-ID: <463379e3-5a31-5064-dd02-ea2fe149fa7e@intel.com>
Date:   Tue, 20 Aug 2019 07:18:06 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Song Liu <songliubraving@...com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Kernel Team <Kernel-team@...com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr by
 PUD_SIZE

On 8/20/19 7:14 AM, Song Liu wrote:
>> *But*, that shouldn't get hit on a Skylake CPU since those have PCIDs
>> and shouldn't have a global kernel image.  Could you confirm whether
>> PCIDs are supported on this CPU?
> Yes, pcid is listed in /proc/cpuinfo. 

So what's going on?  Could you confirm exactly which pti_clone_pgtable()
is causing you problems?  Do you have a theory as to why this manifests
as a performance problem rather than a functional one?

A diff of these:

	/sys/kernel/debug/page_tables/current_user
	/sys/kernel/debug/page_tables/current_kernel

before and after your patch might be helpful.