linux-kernel - Re: External USB disks not recognized with v6.1.8 when using Xen

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Date:   Fri, 3 Feb 2023 17:50:17 +0100 (CET)
From:   Christian Kujau <lists@...dbynature.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Juergen Gross <jgross@...e.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux regressions mailing list <regressions@...ts.linux.dev>
Subject: Re: External USB disks not recognized with v6.1.8 when using Xen

On Thu, 2 Feb 2023, Linus Torvalds wrote:
> So I think that commit should be reverted as broken, and then people
> should *maybe* look at something like this (intentionally whitespace
> damaged, and people should *really* think about what the
> MTRR_TYPE_INVALID case should be - returning UC- is probably what is

Not fully understanding what your proposal really does, I got curious and 
applied it to v6.2-rc6 with 90b926e68f50 (upstream) reverted. And it 
boots, and the disks are there, and the "ioremap error" is gone, but now 
I've got strange memory allocation errors, for like really small 
operations (I wanted to capture dmesg):

  $ dmesg -t | xz -9ec | base64 
  xz: (stdin): Out of memory

With v6.2-rc6 (vanilla, and also booted under Xen) there's no problem 
allocating much more memory than that, so something is still not right. 
Patch applied for reference, but as you said: nobody should apply this :-)

More details:

- https://nerdbynature.de/bits/usb_v6.1.8/dmesg.6.1.8.xen
- https://nerdbynature.de/bits/usb_v6.1.8/dmesg_xen-6.1.8_MTRR_TYPE_INVALID.txt
- https://nerdbynature.de/bits/usb_v6.1.8/meminfo_xen-6.1.8.txt
- https://nerdbynature.de/bits/usb_v6.1.8/meminfo_xen-6.1.8_MTRR_TYPE_INVALID.txt

Thanks,
Christian.
-- 
BOFH excuse #448:

vi needs to be upgraded to vii
View attachment "MTRR_TYPE_INVALID.patch.txt" of type "text/plain" (1317 bytes)