linux-kernel - Re: [PATCH 0/1] x86: restore the write back cache of reserved RAM in iounmap()

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Message-ID: <20201119180206.GA24054@infradead.org>
Date:   Thu, 19 Nov 2020 18:02:06 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Rafael Aquini <aquini@...hat.com>,
        Waiman Long <longman@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1] x86: restore the write back cache of reserved RAM in
 iounmap()

On Thu, Nov 19, 2020 at 12:59:01PM -0500, Andrea Arcangeli wrote:
> Hello everyone,
> 
> We identified some PCD set on the direct mapping causing hardly
> reproducible performance issues and this patch fixes the ultimate root
> cause.
> 
> The caller for now has been tweaked to avoid triggering this case (now
> that we know about it)

What is the callers?  The whole SetPageReservered + ioremap* thing
you mention in the actual patch is completely bogus.  I think we'll
need to reject that as well and fix the caller.