From: "Michał Leszczyński" <michal.leszczynski@cert.pl>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Julien Grall" <julien@xen.org>,
"Kevin Tian" <kevin.tian@intel.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"tamas lengyel" <tamas.lengyel@intel.com>, "Wei Liu" <wl@xen.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Ian Jackson" <ian.jackson@eu.citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>,
"Jun Nakajima" <jun.nakajima@intel.com>,
xen-devel@lists.xenproject.org,
"luwei kang" <luwei.kang@intel.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v4 02/10] x86/vmx: add IPT cpu feature
Date: Thu, 2 Jul 2020 22:29:49 +0200 (CEST) [thread overview]
Message-ID: <1378030024.18497933.1593721789389.JavaMail.zimbra@cert.pl> (raw)
In-Reply-To: <5bb2fb6a-c4f4-7d88-9e07-7922d4235338@suse.com>
----- 2 lip 2020 o 10:34, Jan Beulich jbeulich@suse.com napisał(a):
> On 02.07.2020 10:10, Roger Pau Monné wrote:
>> On Wed, Jul 01, 2020 at 10:42:55PM +0100, Andrew Cooper wrote:
>>> On 30/06/2020 13:33, Michał Leszczyński wrote:
>>>> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
>>>> index ca94c2bedc..b73d824357 100644
>>>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>>>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>>>> @@ -291,6 +291,12 @@ static int vmx_init_vmcs_config(void)
>>>> _vmx_cpu_based_exec_control &=
>>>> ~(CPU_BASED_CR8_LOAD_EXITING | CPU_BASED_CR8_STORE_EXITING);
>>>>
>>>> + rdmsrl(MSR_IA32_VMX_MISC, _vmx_misc_cap);
>>>> +
>>>> + /* Check whether IPT is supported in VMX operation. */
>>>> + vmtrace_supported = cpu_has_ipt &&
>>>> + (_vmx_misc_cap & VMX_MISC_PT_SUPPORTED);
>>>
>>> There is a subtle corner case here. vmx_init_vmcs_config() is called on
>>> all CPUs, and is supposed to level things down safely if we find any
>>> asymmetry.
>>>
>>> If instead you go with something like this:
>>>
>>> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
>>> index b73d824357..6960109183 100644
>>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>>> @@ -294,8 +294,8 @@ static int vmx_init_vmcs_config(void)
>>> rdmsrl(MSR_IA32_VMX_MISC, _vmx_misc_cap);
>>>
>>> /* Check whether IPT is supported in VMX operation. */
>>> - vmtrace_supported = cpu_has_ipt &&
>>> - (_vmx_misc_cap & VMX_MISC_PT_SUPPORTED);
>>> + if ( !(_vmx_misc_cap & VMX_MISC_PT_SUPPORTED) )
>>> + vmtrace_supported = false;
>>
>> This is also used during hotplug, so I'm not sure it's safe to turn
>> vmtrace_supported off during runtime, where VMs might be already using
>> it. IMO it would be easier to just set it on the BSP, and then refuse
>> to bring up any AP that doesn't have the feature.
>
> +1
>
> IOW I also don't think that "vmx_init_vmcs_config() ... is supposed to
> level things down safely". Instead I think the expectation is for
> CPU onlining to fail if a CPU lacks features compared to the BSP. As
> can be implied from what Roger says, doing like what you suggest may
> be fine during boot, but past that only at times where we know there's
> no user of a certain feature, and where discarding the feature flag
> won't lead to other inconsistencies (which may very well mean "never").
>
> Jan
Ok, I will modify it in a way Roger suggested for the previous patch
version. CPU onlining will fail if there is an inconsistency.
Best regards,
Michał Leszczyński
CERT Polska
next prev parent reply other threads:[~2020-07-02 20:30 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-30 12:33 [PATCH v4 00/10] Implement support for external IPT monitoring Michał Leszczyński
2020-06-30 12:33 ` [PATCH v4 01/10] x86/vmx: add Intel PT MSR definitions Michał Leszczyński
2020-06-30 16:23 ` Jan Beulich
2020-06-30 17:37 ` Andrew Cooper
2020-06-30 18:03 ` Tamas K Lengyel
2020-06-30 18:27 ` Michał Leszczyński
2020-07-01 17:52 ` Andrew Cooper
2020-06-30 12:33 ` [PATCH v4 02/10] x86/vmx: add IPT cpu feature Michał Leszczyński
2020-07-01 9:49 ` Roger Pau Monné
2020-07-01 15:12 ` Julien Grall
2020-07-01 16:06 ` Andrew Cooper
2020-07-01 16:17 ` Julien Grall
2020-07-01 16:18 ` Julien Grall
2020-07-01 17:26 ` Andrew Cooper
2020-07-01 18:02 ` Julien Grall
2020-07-01 18:06 ` Andrew Cooper
2020-07-01 18:09 ` Julien Grall
2020-07-02 8:29 ` Jan Beulich
2020-07-02 8:42 ` Julien Grall
2020-07-02 8:50 ` Jan Beulich
2020-07-02 8:54 ` Julien Grall
2020-07-02 9:18 ` Jan Beulich
2020-07-02 9:57 ` Julien Grall
2020-07-02 13:30 ` Jan Beulich
2020-07-02 14:14 ` Julien Grall
2020-07-02 14:17 ` Jan Beulich
2020-07-02 14:31 ` Julien Grall
2020-07-02 20:28 ` Michał Leszczyński
2020-07-03 7:58 ` Julien Grall
2020-07-04 19:16 ` Michał Leszczyński
2020-07-01 21:42 ` Andrew Cooper
2020-07-02 8:10 ` Roger Pau Monné
2020-07-02 8:34 ` Jan Beulich
2020-07-02 20:29 ` Michał Leszczyński [this message]
2020-06-30 12:33 ` [PATCH v4 03/10] tools/libxl: add vmtrace_pt_size parameter Michał Leszczyński
2020-07-01 10:05 ` Roger Pau Monné
2020-07-02 9:00 ` Roger Pau Monné
2020-07-02 16:23 ` Michał Leszczyński
2020-07-03 9:44 ` Roger Pau Monné
2020-07-03 9:56 ` Jan Beulich
2020-07-03 10:11 ` Roger Pau Monné
2020-07-04 17:23 ` Julien Grall
2020-07-06 8:46 ` Jan Beulich
2020-07-07 8:44 ` Julien Grall
2020-07-07 9:10 ` Jan Beulich
2020-07-07 9:16 ` Julien Grall
2020-07-07 11:17 ` Michał Leszczyński
2020-07-07 11:21 ` Jan Beulich
2020-07-07 11:35 ` Michał Leszczyński
2020-07-02 10:24 ` Anthony PERARD
2020-07-04 17:48 ` Julien Grall
2020-06-30 12:33 ` [PATCH v4 04/10] x86/vmx: implement processor tracing for VMX Michał Leszczyński
2020-07-01 10:30 ` Roger Pau Monné
2020-06-30 12:33 ` [PATCH v4 05/10] common/domain: allocate vmtrace_pt_buffer Michał Leszczyński
2020-07-01 10:38 ` Roger Pau Monné
2020-07-01 15:35 ` Julien Grall
2020-06-30 12:33 ` [PATCH v4 06/10] memory: batch processing in acquire_resource() Michał Leszczyński
2020-07-01 10:46 ` Roger Pau Monné
2020-07-03 10:35 ` Julien Grall
2020-07-03 10:52 ` Paul Durrant
2020-07-03 11:17 ` Julien Grall
2020-07-03 11:22 ` Jan Beulich
2020-07-03 11:36 ` Julien Grall
2020-07-03 12:50 ` Jan Beulich
2020-07-03 11:40 ` Paul Durrant
2020-06-30 12:33 ` [PATCH v4 07/10] x86/mm: add vmtrace_buf resource type Michał Leszczyński
2020-07-01 10:52 ` Roger Pau Monné
2020-06-30 12:33 ` [PATCH v4 08/10] x86/domctl: add XEN_DOMCTL_vmtrace_op Michał Leszczyński
2020-07-01 11:00 ` Roger Pau Monné
2020-06-30 12:33 ` [PATCH v4 09/10] tools/libxc: add xc_vmtrace_* functions Michał Leszczyński
2020-07-21 10:52 ` Wei Liu
2020-06-30 12:33 ` [PATCH v4 10/10] tools/proctrace: add proctrace tool Michał Leszczyński
2020-07-02 15:10 ` Andrew Cooper
2020-07-21 10:52 ` Wei Liu
2020-06-30 12:48 ` [PATCH v4 00/10] Implement support for external IPT monitoring Hubert Jasudowicz
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