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Date:   Mon, 13 May 2019 13:30:06 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nadav Amit <namit@vmware.com>
Cc:     Yang Shi <yang.shi@linux.alibaba.com>,
        "jstancek@redhat.com" <jstancek@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
        Nick Piggin <npiggin@gmail.com>,
        Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] mm: mmu_gather: remove __tlb_reset_range() for force
 flush
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On Mon, May 13, 2019 at 09:11:38AM +0000, Nadav Amit wrote:
> BTW: sometimes you don’t see the effect of these full TLB flushes as much in
> VMs. I encountered a strange phenomenon at the time - INVLPG for an
> arbitrary page cause my Haswell machine flush the entire TLB, when the
> INVLPG was issued inside a VM. It took me quite some time to analyze this
> problem. Eventually Intel told me that’s part of what is called “page
> fracturing” - if the host uses 4k pages in the EPT, they (usually) need to
> flush the entire TLB for any INVLPG. That’s happens since they don’t know
> the size of the flushed page.

Cute... if only they'd given us an interface to tell them... :-)