From: Paolo Bonzini <pbonzini@redhat.com>
To: Borislav Petkov <bp@alien8.de>, "Luck, Tony" <tony.luck@intel.com>
Cc: Jim Mattson <jmattson@google.com>, Qian Cai <cai@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>, x86 <x86@kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH] x86/mce: Check for hypervisor before enabling additional error logging
Date: Tue, 10 Nov 2020 09:50:43 +0100 [thread overview]
Message-ID: <094c2395-b1b3-d908-657c-9bd4144e40ac@redhat.com> (raw)
In-Reply-To: <20201110063151.GB7290@nazgul.tnic>
On 10/11/20 07:31, Borislav Petkov wrote:
>>
>> + if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
>> + return;
>> +
> Frankly, I'm tired of wagging the dog because the tail can't. If
> qemu/kvm can't emulate a CPU model fully then it should ignore those
> unknown MSR accesses by default, i.e., that "ignore_msrs" functionality
> should be on by default I'd say...
>
> We certainly can't be sprinkling this check everytime the kernel tries
> to do something as basic as read an MSR.
You don't have to, also because it's wrong. Fortunately it's much
simpler than that:
1) ignore_msrs _cannot_ be on by default. You cannot know in advance
that for all non-architectural MSRs it's okay for them to read as zero
and eat writes. For some non-architectural MSR which never reads as
zero on real hardware, who knows that there isn't some code using the
contents of the MSR as a divisor, and causing a division by zero
exception with ignore_msrs=1?
2) it's not just KVM. _Any_ hypervisor is bound to have this issue for
some non-architectural MSRs. KVM just gets the flak because Linux CI
environments (for obvious reasons) use it more than they use Hyper-V or
ESXi or VirtualBox.
3) because of (1) and (2), the solution is very simple. If the MSR is
architectural, its absence is a KVM bug and we'll fix it in all stable
versions. If the MSR is not architectural (and 17Fh isn't; not only
it's not mentioned in the SDM, even Google is failing me), never ever
assume that the CPUID family/model/stepping implies a given MSR is
there, and just use rdmsr_safe/wrmsr_safe.
So, for this patch,
Nacked-by: Paolo Bonzini <pbonzini@redhat.com>
Paolo
next prev parent reply other threads:[~2020-11-10 8:50 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <fcb21490-84a1-8b99-b494-3a6ac2a0e16a@skynet.be>
[not found] ` <20201029100655.GA31903@zn.tnic>
[not found] ` <20201029151518.GA23990@agluck-desk2.amr.corp.intel.com>
[not found] ` <20201029194118.GC31903@zn.tnic>
[not found] ` <87ft5wo8zn.fsf@nanos.tec.linutronix.de>
[not found] ` <20201030091056.GA6532@zn.tnic>
[not found] ` <20201030190400.GA13797@agluck-desk2.amr.corp.intel.com>
2020-10-30 19:08 ` [PATCH] x86/mce: Enable additional error logging on certain Intel CPUs Luck, Tony
2020-11-02 11:12 ` Borislav Petkov
2020-11-02 11:18 ` [tip: ras/core] " tip-bot2 for Tony Luck
2020-11-09 21:55 ` Qian Cai
2020-11-09 22:09 ` Luck, Tony
2020-11-09 22:36 ` Jim Mattson
2020-11-09 22:57 ` Luck, Tony
2020-11-09 23:24 ` [PATCH] x86/mce: Check for hypervisor before enabling additional error logging Luck, Tony
2020-11-10 6:31 ` Borislav Petkov
2020-11-10 8:50 ` Paolo Bonzini [this message]
2020-11-10 9:56 ` Borislav Petkov
2020-11-10 10:40 ` Paolo Bonzini
2020-11-10 15:50 ` Borislav Petkov
2020-11-10 16:08 ` Paolo Bonzini
2020-11-10 17:52 ` Luck, Tony
2020-11-10 20:37 ` Paolo Bonzini
2020-11-11 0:39 ` [PATCH v2] x86/mce: Use "safe" MSR functions when " Luck, Tony
2020-11-16 16:44 ` [tip: ras/core] " tip-bot2 for Tony Luck
2020-11-09 23:26 ` [tip: ras/core] x86/mce: Enable additional error logging on certain Intel CPUs Jim Mattson
2020-11-09 23:36 ` Luck, Tony
2020-11-10 9:10 ` Paolo Bonzini
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=094c2395-b1b3-d908-657c-9bd4144e40ac@redhat.com \
--to=pbonzini@redhat.com \
--cc=bp@alien8.de \
--cc=cai@redhat.com \
--cc=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=tony.luck@intel.com \
--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).