From: Thorsten Leemhuis <regressions@leemhuis.info>
To: Juergen Gross <jgross@suse.com>,
xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Cc: brchuckz@netscape.net, jbeulich@suse.com,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"# 5 . 17" <stable@vger.kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Pavel Machek <pavel@ucw.cz>, Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH 0/3] x86: make pat and mtrr independent from each other
Date: Sun, 17 Jul 2022 09:55:00 +0200 [thread overview]
Message-ID: <efbde93b-e280-0e40-798d-dc7bf8ca83cf@leemhuis.info> (raw)
In-Reply-To: <20220715142549.25223-1-jgross@suse.com>
Hi Juergen!
On 15.07.22 16:25, Juergen Gross wrote:
> Today PAT can't be used without MTRR being available, unless MTRR is at
> least configured via CONFIG_MTRR and the system is running as Xen PV
> guest. In this case PAT is automatically available via the hypervisor,
> but the PAT MSR can't be modified by the kernel and MTRR is disabled.
>
> As an additional complexity the availability of PAT can't be queried
> via pat_enabled() in the Xen PV case, as the lack of MTRR will set PAT
> to be disabled. This leads to some drivers believing that not all cache
> modes are available, resulting in failures or degraded functionality.
>
> The same applies to a kernel built with no MTRR support: it won't
> allow to use the PAT MSR, even if there is no technical reason for
> that, other than setting up PAT on all cpus the same way (which is a
> requirement of the processor's cache management) is relying on some
> MTRR specific code.
>
> Fix all of that by:
>
> - moving the function needed by PAT from MTRR specific code one level
> up
> - adding a PAT indirection layer supporting the 3 cases "no or disabled
> PAT", "PAT under kernel control", and "PAT under Xen control"
> - removing the dependency of PAT on MTRR
Thx for working on this. If you need to respin these patches for one
reason or another, could you do me a favor and add proper 'Link:' tags
pointing to all reports about this issue? e.g. like this:
Link: https://lore.kernel.org/regressions/YnHK1Z3o99eMXsVK@mail-itl/
These tags are considered important by Linus[1] and others, as they
allow anyone to look into the backstory weeks or years from now. That is
why they should be placed in cases like this, as
Documentation/process/submitting-patches.rst and
Documentation/process/5.Posting.rst explain in more detail. I care
personally, because these tags make my regression tracking efforts a
whole lot easier, as they allow my tracking bot 'regzbot' to
automatically connect reports with patches posted or committed to fix
tracked regressions.
[1] see for example:
https://lore.kernel.org/all/CAHk-=wjMmSZzMJ3Xnskdg4+GGz=5p5p+GSYyFBTh0f-DgvdBWg@mail.gmail.com/
https://lore.kernel.org/all/CAHk-=wgs38ZrfPvy=nOwVkVzjpM3VFU1zobP37Fwd_h9iAD5JQ@mail.gmail.com/
https://lore.kernel.org/all/CAHk-=wjxzafG-=J8oT30s7upn4RhBs6TX-uVFZ5rME+L5_DoJA@mail.gmail.com/
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.
BTW, let me tell regzbot to monitor this thread:
#regzbot ^backmonitor:
https://lore.kernel.org/regressions/YnHK1Z3o99eMXsVK@mail-itl/
next prev parent reply other threads:[~2022-07-17 7:55 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 14:25 [PATCH 0/3] x86: make pat and mtrr independent from each other Juergen Gross
2022-07-15 14:25 ` [PATCH 1/3] x86: move some code out of arch/x86/kernel/cpu/mtrr Juergen Gross
2022-07-18 12:20 ` Borislav Petkov
2022-07-15 14:25 ` [PATCH 2/3] x86: add wrapper functions for mtrr functions handling also pat Juergen Gross
2022-07-15 16:41 ` Rafael J. Wysocki
2022-07-19 10:47 ` Borislav Petkov
2022-07-15 14:25 ` [PATCH 3/3] x86: decouple pat and mtrr handling Juergen Gross
2022-07-19 15:15 ` Borislav Petkov
2022-08-13 16:56 ` PING " Chuck Zmudzinski
2022-08-13 17:20 ` Borislav Petkov
2022-08-13 21:40 ` Chuck Zmudzinski
2022-08-13 21:48 ` Borislav Petkov
2022-08-13 22:41 ` Chuck Zmudzinski
2022-08-16 18:31 ` Chuck Zmudzinski
2022-08-17 9:17 ` Juergen Gross
2022-07-20 1:12 ` Chuck Zmudzinski
2022-07-16 11:32 ` [PATCH 0/3] x86: make pat and mtrr independent from each other Chuck Zmudzinski
2022-07-16 11:42 ` Borislav Petkov
2022-07-17 4:06 ` Chuck Zmudzinski
2022-07-16 12:01 ` Chuck Zmudzinski
2022-07-17 7:55 ` Thorsten Leemhuis [this message]
2022-07-18 11:32 ` Chuck Zmudzinski
2022-07-19 13:16 ` Chuck Zmudzinski
2022-08-13 16:56 ` Chuck Zmudzinski
2022-08-14 7:42 ` Chuck Zmudzinski
2022-08-14 8:08 ` Juergen Gross
2022-08-15 3:23 ` Chuck Zmudzinski
2022-08-15 16:56 ` Chuck Zmudzinski
2022-08-15 18:00 ` Thorsten Leemhuis
2022-08-15 18:17 ` Chuck Zmudzinski
2022-08-16 14:41 ` Thorsten Leemhuis
2022-08-16 16:16 ` Chuck Zmudzinski
2022-08-16 16:53 ` Thorsten Leemhuis
2022-08-16 17:28 ` Chuck Zmudzinski
2022-08-18 18:54 ` Chuck Zmudzinski
2022-08-14 9:19 ` Chuck Zmudzinski
2022-08-14 9:50 ` Greg KH
2022-08-14 12:08 ` Chuck Zmudzinski
2022-08-14 13:01 ` Greg KH
2022-08-14 16:03 ` Chuck Zmudzinski
2022-08-14 19:52 ` Chuck Zmudzinski
2022-08-15 16:04 ` Chuck Zmudzinski
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