From: Paolo Bonzini <pbonzini@redhat.com>
To: Eduardo Habkost <ehabkost@redhat.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Jonathan Corbet <corbet@lwn.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Randy Dunlap <rdunlap@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Maciej W. Rozycki" <macro@orcam.me.uk>,
Viresh Kumar <viresh.kumar@linaro.org>,
Vlastimil Babka <vbabka@suse.cz>, Tony Luck <tony.luck@intel.com>,
Sean Christopherson <seanjc@google.com>,
Kyung Min Park <kyung.min.park@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Juergen Gross <jgross@suse.com>,
Krish Sadhukhan <krish.sadhukhan@oracle.com>,
Kan Liang <kan.liang@linux.intel.com>,
Joerg Roedel <jroedel@suse.de>,
Victor Ding <victording@google.com>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
Brijesh Singh <brijesh.singh@amd.com>,
Dave Hansen <dave.hansen@intel.com>,
Mike Rapoport <rppt@kernel.org>,
Anthony Steinhauser <asteinhauser@google.com>,
Anand K Mistry <amistry@google.com>,
Andi Kleen <ak@linux.intel.com>, Miguel Ojeda <ojeda@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Joe Perches <joe@perches.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-perf-users@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE
Date: Tue, 6 Jul 2021 23:05:47 +0200 [thread overview]
Message-ID: <4cc2c5fe-2153-05c5-dedd-8cb650753740@redhat.com> (raw)
In-Reply-To: <20210706195233.h6w4cm73oktfqpgz@habkost.net>
On 06/07/21 21:52, Eduardo Habkost wrote:
> On Wed, Jun 09, 2021 at 02:14:39PM -0700, Pawan Gupta wrote:
>> On CPUs that deprecated TSX, clearing the enumeration bits CPUID.RTM and
>> CPUID.HLE may not be desirable in some corner cases. Like a saved guest
>> would refuse to resume if it was saved before the microcode update
>> that deprecated TSX.
> Why is a global option necessary to allow those guests to be
> resumed? Why can't KVM_GET_SUPPORTED_CPUID always return the HLE
> and RTM bits as supported when the host CPU has them?
It's a bit tricky, because HLE and RTM won't really behave well. An old
guest that sees RTM=1 might end up retrying and aborting transactions
too much. So I'm not sure that a QEMU "-cpu host" guest should have HLE
and RTM enabled.
So it makes sense to handle it in userspace, with one of the two
following possibilities:
- userspace sees TSX_FORCE_ABORT and if so it somehow "discourages"
setting HLE/RTM, even though they are shown as supported
- userspace sees TSX_FORCE_ABORT and if so it knows HLE/RTM can be set,
even though they are discouraged in general
In any case, KVM's "supported CPUID" is based on the host features but
independent. KVM can decide to show or hide the hardware HLE and RTM
bits independent of the host tsx= setting; it may make sense to hide the
bits via a module parameter, but in any case this patch is not needed.
Paolo
next prev parent reply other threads:[~2021-07-06 21:05 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-09 20:57 [PATCH 0/4] TSX force abort Pawan Gupta
2021-06-09 20:58 ` [PATCH 1/4] x86/msr: Define new bits in TSX_FORCE_ABORT MSR Pawan Gupta
2021-06-11 8:39 ` Borislav Petkov
2021-06-11 21:31 ` Pawan Gupta
2021-06-09 21:12 ` [PATCH 2/4] perf/x86/intel: Do not deploy workaround when TSX is deprecated Pawan Gupta
2021-06-11 7:50 ` Borislav Petkov
2021-06-11 21:34 ` Pawan Gupta
2021-06-11 22:01 ` Borislav Petkov
2021-06-11 23:21 ` Pawan Gupta
2021-06-09 21:13 ` [PATCH 3/4] x86/tsx: Clear CPUID bits when TSX always force aborts Pawan Gupta
2021-06-11 10:03 ` Borislav Petkov
2021-06-11 21:36 ` Pawan Gupta
2021-06-09 21:14 ` [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE Pawan Gupta
2021-06-11 10:06 ` Borislav Petkov
2021-06-11 21:37 ` Pawan Gupta
2021-07-06 19:52 ` Eduardo Habkost
2021-07-06 21:05 ` Paolo Bonzini [this message]
2021-07-06 21:33 ` Eduardo Habkost
2021-07-06 21:58 ` Paolo Bonzini
2021-07-07 15:08 ` Eduardo Habkost
2021-07-07 16:42 ` Jim Mattson
2021-07-07 17:08 ` Eduardo Habkost
2021-07-07 17:15 ` Jim Mattson
2021-07-07 18:23 ` Eduardo Habkost
2021-07-08 9:15 ` Paolo Bonzini
2021-07-06 21:16 ` Pawan Gupta
2021-07-06 21:19 ` Eduardo Habkost
2021-07-06 22:51 ` Pawan Gupta
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=4cc2c5fe-2153-05c5-dedd-8cb650753740@redhat.com \
--to=pbonzini@redhat.com \
--cc=acme@kernel.org \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=amistry@google.com \
--cc=asteinhauser@google.com \
--cc=bp@alien8.de \
--cc=brijesh.singh@amd.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@intel.com \
--cc=ehabkost@redhat.com \
--cc=fenghua.yu@intel.com \
--cc=hpa@zytor.com \
--cc=jgross@suse.com \
--cc=joe@perches.com \
--cc=jolsa@redhat.com \
--cc=jroedel@suse.de \
--cc=kan.liang@linux.intel.com \
--cc=krish.sadhukhan@oracle.com \
--cc=kvm@vger.kernel.org \
--cc=kyung.min.park@intel.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=macro@orcam.me.uk \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=ndesaulniers@google.com \
--cc=ojeda@kernel.org \
--cc=paulmck@kernel.org \
--cc=pawan.kumar.gupta@linux.intel.com \
--cc=peterz@infradead.org \
--cc=rdunlap@infradead.org \
--cc=ricardo.neri-calderon@linux.intel.com \
--cc=rppt@kernel.org \
--cc=seanjc@google.com \
--cc=srinivas.pandruvada@linux.intel.com \
--cc=tglx@linutronix.de \
--cc=thomas.lendacky@amd.com \
--cc=tony.luck@intel.com \
--cc=vbabka@suse.cz \
--cc=victording@google.com \
--cc=viresh.kumar@linaro.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