From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, KVM list <kvm@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, xen-devel <Xen-devel@lists.xen.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [Xen-devel] [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops
Date: Thu, 17 Sep 2015 11:11:54 -0400 [thread overview]
Message-ID: <55FAD83A.3010307@oracle.com> (raw)
In-Reply-To: <55FA8381.5010604@citrix.com>
On 09/17/2015 05:10 AM, Andrew Cooper wrote:
> On 17/09/15 00:33, Andy Lutomirski wrote:
>> Setting CONFIG_PARAVIRT=y has an unintended side effect: it silently
>> turns all rdmsr and wrmsr operations into the safe variants without
>> any checks that the operations actually succeed.
>>
>> This is IMO awful: it papers over bugs. In particular, KVM gueests
>> might be unwittingly depending on this behavior because
>> CONFIG_KVM_GUEST currently depends on CONFIG_PARAVIRT. I'm not
>> aware of any such problems, but applying this series would be a good
>> way to shake them out.
>>
>> Fix it so that the MSR operations work the same on CONFIG_PARAVIRT=n
>> and CONFIG_PARAVIRT=y as long as Xen isn't being used. The Xen
>> maintainers are welcome to make a similar change on top of this.
> The Xen side of things need some further modification before this would
> be a safe operation to perform.
>
> On the wrmsr side of things alone, this is the list of things Xen
> currently objects to and injects #GP faults for.
>
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000081 from
> 0xe023e00800000000 to 0x0023001000000000.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000082 from
> 0xffff82d0bffff000 to 0xffffffff81560060.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000083 from
> 0xffff82d0bffff020 to 0xffffffff81558100.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 0000000000000174 from
> 0x000000000000e008 to 0x0000000000000010.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 0000000000000175 from
> 0xffff8300ac0f7fc0 to 0x0000000000000000.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 0000000000000176 from
> 0xffff82d08023fd50 to 0xffffffff815616d0.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000083 from
> 0xffff82d0bffff020 to 0xffffffff81561910.
> (XEN) traps.c:2692:d0v0 Domain attempted WRMSR 00000000c0000084 from
> 0x0000000000074700 to 0x0000000000047700.
>
> However, it would be certainly be worth teaching PVops not to play with
> MSRs it doesn't own.
PVops already knows about those. There is even has a comment about how
we shouldn't touch those MSRs. And yet three lines later we still write
them.
-boris
prev parent reply other threads:[~2015-09-17 15:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-16 23:33 [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Andy Lutomirski
2015-09-16 23:33 ` [PATCH 1/3] x86/paravirt: Add _safe to the read_msr and write_msr PV hooks Andy Lutomirski
2015-09-16 23:33 ` [PATCH 2/3] x86/paravirt: Add paravirt_{read,write}_msr Andy Lutomirski
2015-09-16 23:33 ` [PATCH 3/3] x86/paravirt: Make "unsafe" MSR accesses unsafe even if PARAVIRT=y Andy Lutomirski
2015-09-17 7:19 ` [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops Ingo Molnar
2015-09-17 9:31 ` Borislav Petkov
2015-09-17 11:22 ` H. Peter Anvin
2015-09-17 11:39 ` Paolo Bonzini
2015-09-17 15:27 ` Borislav Petkov
2015-09-17 15:32 ` [Xen-devel] " Andrew Cooper
2015-09-17 15:37 ` Borislav Petkov
2015-09-17 15:23 ` Andy Lutomirski
2015-09-17 15:27 ` Arjan van de Ven
2015-09-17 15:29 ` Paolo Bonzini
2015-09-17 15:31 ` Arjan van de Ven
2015-09-17 15:33 ` Paolo Bonzini
2015-09-17 17:30 ` Ingo Molnar
2015-09-17 18:51 ` Andy Lutomirski
2015-09-17 8:58 ` Peter Zijlstra
2015-09-17 11:40 ` Paolo Bonzini
2015-09-17 12:27 ` Peter Zijlstra
2015-09-17 15:17 ` Andy Lutomirski
2015-09-17 15:17 ` Peter Zijlstra
2015-09-17 15:26 ` Andy Lutomirski
2015-09-17 15:29 ` Paolo Bonzini
2015-09-17 9:10 ` [Xen-devel] " Andrew Cooper
2015-09-17 15:11 ` Boris Ostrovsky [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=55FAD83A.3010307@oracle.com \
--to=boris.ostrovsky@oracle.com \
--cc=Xen-devel@lists.xen.org \
--cc=andrew.cooper3@citrix.com \
--cc=arjan@linux.intel.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).