From: Paolo Bonzini <pbonzini@redhat.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
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 23:58:08 +0200 [thread overview]
Message-ID: <671be35f-220a-f583-aa31-3a2da7dae93a@redhat.com> (raw)
In-Reply-To: <CAOpTY_qdbbnauTkbjkz+cZmo8=Hz6qqLNY6i6uamqhcty=Q1sw@mail.gmail.com>
On 06/07/21 23:33, Eduardo Habkost wrote:
> On Tue, Jul 6, 2021 at 5:05 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>> 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.
>
> Is the purpose of GET_SUPPORTED_CPUID to return what is supported by
> KVM, or to return what "-cpu host" should enable by default? They are
> conflicting requirements in this case.
In theory there is GET_EMULATED_CPUID for the former, so it should be
the latter. In practice neither QEMU nor Libvirt use it; maybe now we
have a good reason to add it, but note that userspace could also check
host RTM_ALWAYS_ABORT.
> Returning HLE=1,RTM=1 in GET_SUPPORTED_CPUID makes existing userspace
> take bad decisions until it's updated.
>
> Returning HLE=0,RTM=0 in GET_SUPPORTED_CPUID prevents existing
> userspace from resuming existing VMs (despite being technically
> possible).
>
> The first option has an easy workaround that doesn't require a
> software update (disabling HLE/RTM in the VM configuration). The
> second option doesn't have a workaround. I'm inclined towards the
> first option.
The default has already been tsx=off for a while though, so checking
either GET_EMULATED_CPUID or host RTM_ALWAYS_ABORT in userspace might
also be feasible for those that are still on tsx=on.
Paolo
next prev parent reply other threads:[~2021-07-06 21:58 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
2021-07-06 21:33 ` Eduardo Habkost
2021-07-06 21:58 ` Paolo Bonzini [this message]
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=671be35f-220a-f583-aa31-3a2da7dae93a@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;
as well as URLs for NNTP newsgroup(s).