linux-kernel - Re: [PATCH v2 00/25] Enable FRED with KVM VMX

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Date: Wed, 27 Mar 2024 08:08:14 +0000
From: "Kang, Shan" <shan.kang@...el.com>
To: "Li, Xin3" <xin3.li@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-kselftest@...r.kernel.org"
	<linux-kselftest@...r.kernel.org>
CC: "corbet@....net" <corbet@....net>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "x86@...nel.org" <x86@...nel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
	"mingo@...hat.com" <mingo@...hat.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "hpa@...or.com" <hpa@...or.com>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "peterz@...radead.org" <peterz@...radead.org>,
	"shuah@...nel.org" <shuah@...nel.org>, "Shankar, Ravi V"
	<ravi.v.shankar@...el.com>, "xin@...or.com" <xin@...or.com>
Subject: Re: [PATCH v2 00/25] Enable FRED with KVM VMX

On Wed, 2024-02-07 at 09:26 -0800, Xin Li wrote:
> This patch set enables the Intel flexible return and event delivery
> (FRED) architecture with KVM VMX to allow guests to utilize FRED.
> 
We tested this FRED KVM patch set on a 7th Intel(R) Core(TM) CPU and the Intel 
Simics® Simulator with the following four configurations:

The first config is the baseline on bare metal.
The second config is the baseline on Intel Simics® Simulator.
The third config enables host FRED, but disables guest FRED.
The last config enables both host and guest FRED.

Following are the Kselftest results on KVM guests.

+---------------------------------------------+-------+-------+-------+-------+
|                  Config                     |  Pass |  Fail |  Skip |  Hang |
+---------------------------------------------+-------+-------+-------+-------+
|the 7th Intel(R) Core(TM) CPU                |       |       |       |       |
|  L0: 6.8.0-rc3+ w/ FRED native/KVM patch set|  1775 |  526  |  332  |   6   |
|  L1: 6.8.0-rc3+                             |       |       |       |       |
+---------------------------------------------+-------+-------+-------+-------+
|Intel Simics® Simulator w/o FRED model       |       |       |       |       |
|  L0: 6.8.0-rc3+ w/ FRED native/KVM patch set|  1770 |  526  |  331  |   12  |
|  L1: 6.8.0-rc3+ w/ FRED native/KVM patch set|       |       |       |       |
+---------------------------------------------+-------+-------+-------+-------+
|Intel Simics® Simulator w/ FRED model        |       |       |       |       |
|  L0: 6.8.0-rc3+ w/ FRED native/KVM patch set|  1770 |  526  |  331  |   12  |
|  L1: 6.8.0-rc3+ w/ FRED native/KVM patch set|       |       |       |       |
|         but FRED disabled                   |       |       |       |       |
+---------------------------------------------+-------+-------+-------+-------+
|Intel Simics® Simulator w/ FRED model        |       |       |       |       |
|  L0: 6.8.0-rc3+ w/ FRED native/KVM patch set|  1769 |  528  |  330  |   12  |
|  L1: 6.8.0-rc3+ w/ FRED native/KVM patch set|       |       |       |       |
+---------------------------------------------+-------+-------+-------+-------+

First of all we don't see any major issue. One major differences come from
perf tests. Another variances are from timer tests due to Intel Simics®
emulator's slowness.

The tests "x86:sysret_rip_64" and "x86:sigreturn_32" fail on the last config,
because they are not valid tests for FRED:
https://lore.kernel.org/lkml/20230220030959.119222-1-ammarfaizi2@gnuweeb.org/T/#u
https://lore.kernel.org/lkml/20230706052231.2183-1-xin3.li@intel.com/

NB: Some tests pass on Intel Simics® emulator, but not bare metal. If needed,
we can share the data.

We conducted local live migration tests with LKGS/FRED/WRMSRNS enabled/disabled
on Intel Simics® Simulator, and see no problems.

We also tested KVM Kselftest on a nested FRED KVM guest, 48 out of 83 cases
passed and the rest cases failed due to the slowness of Intel Simics® emulator.

Detailed report upon request.