linux-kernel - Re: [PATCH] mm: Keep memory type same on DEVMEM Page-Fault

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Message-Id: <20230416113944.c9b50a76a98b9e7c974cfac9@linux-foundation.org>
Date:   Sun, 16 Apr 2023 11:39:44 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "buddy.zhang" <buddy.zhang@...cuitos.cn>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Venkatesh Pallipadi <venki@...gle.com>,
        Suresh Siddha <sbsiddha@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Konstantin Khlebnikov <khlebnikov@...nvz.org>
Subject: Re: [PATCH] mm: Keep memory type same on DEVMEM Page-Fault

On Wed, 12 Apr 2023 14:22:36 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Sun, 19 Mar 2023 11:37:50 +0800 "buddy.zhang" <buddy.zhang@...cuitos.cn> wrote:
> 
> > On X86 architecture, supports memory type on Page-table, such as
> > PTE is PAT/PCD/PWD, which can setup up Memory Type as WC/WB/WT/UC etc.
> > Then, Virtual address from userspace or kernel space can map to
> > same physical page, if each page table has different memory type,
> > then it's confused to have more memory type for same physical page.
> 
> Thanks.  Nobody has worked on this code for a long time.  I'll cc a few
> folks who may be able to comment.
> 

Well that didn't go very well.

Buddy, can you please explain what are the user-visible effects of the
bug?  Does the kernel crash?  Memory corruption, etc?  Thanks.