From: Jan Beulich <jbeulich@suse.com>
To: "Jürgen Groß" <jgross@suse.com>
Cc: "Kevin Tian" <kevin.tian@intel.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Julien Grall" <julien@xen.org>, "Wei Liu" <wl@xen.org>,
"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
"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,
"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v6 09/12] xen: add runtime parameter access support to hypfs
Date: Fri, 6 Mar 2020 10:04:49 +0100 [thread overview]
Message-ID: <ca0ee3e7-bd09-bdeb-da6a-f4acaa96f27a@suse.com> (raw)
In-Reply-To: <0b6e7f36-786c-f788-0c13-7e0ed41d77df@suse.com>
On 06.03.2020 09:47, Jürgen Groß wrote:
> On 06.03.20 09:20, Jan Beulich wrote:
>> On 06.03.2020 07:42, Jürgen Groß wrote:
>>> On 05.03.20 09:26, Jan Beulich wrote:
>>>> On 05.03.2020 07:01, Jürgen Groß wrote:
>>>>> On 04.03.20 17:56, Jan Beulich wrote:
>>>>>> On 04.03.2020 17:31, Jürgen Groß wrote:
>>>>>>> On 04.03.20 16:19, Jan Beulich wrote:
>>>>>>>> On 04.03.2020 16:07, Jürgen Groß wrote:
>>>>>>>>> On 04.03.20 12:32, Jan Beulich wrote:
>>>>>>>>>> On 26.02.2020 13:47, Juergen Gross wrote:
>>>>>>>>>>> +static void update_ept_param_append(const char *str, int val)
>>>>>>>>>>> +{
>>>>>>>>>>> + char *pos = opt_ept_setting + strlen(opt_ept_setting);
>>>>>>>>>>> +
>>>>>>>>>>> + snprintf(pos, sizeof(opt_ept_setting) - (pos - opt_ept_setting),
>>>>>>>>>>> + ",%s=%d", str, val);
>>>>>>>>>>> +}
>>>>>>>>>>> +
>>>>>>>>>>> +static void update_ept_param(void)
>>>>>>>>>>> +{
>>>>>>>>>>> + snprintf(opt_ept_setting, sizeof(opt_ept_setting), "pml=%d", opt_ept_pml);
>>>>>>>>>>> + if ( opt_ept_ad >= 0 )
>>>>>>>>>>> + update_ept_param_append("ad", opt_ept_ad);
>>>>>>>>>>
>>>>>>>>>> This won't correctly reflect reality: If you look at
>>>>>>>>>> vmx_init_vmcs_config(), even a negative value means "true" here,
>>>>>>>>>> unless on a specific Atom model. I think init_ept_param() wants
>>>>>>>>>> to have that erratum workaround logic moved there, such that
>>>>>>>>>> you can then assme the value to be non-negative here.
>>>>>>>>>
>>>>>>>>> But isn't not mentioning it in the -1 case correct? -1 means: do the
>>>>>>>>> correct thing on the current hardware.
>>>>>>>>
>>>>>>>> Well, I think the output here should represent effective settings,
>>>>>>>
>>>>>>> The minimum requirement is to reflect the effective parameters, like
>>>>>>> cmdline is doing for boot-time only parameters. With runtime parameters
>>>>>>> we had no way of telling what was set, and this is now possible.
>>>>>>>
>>>>>>>> and a sub-item should be suppressed only if a setting has no effect
>>>>>>>> at all in the current setup, like ...
>>>>>>>>
>>>>>>>>>>> + if ( opt_ept_exec_sp >= 0 )
>>>>>>>>>>> + update_ept_param_append("exec-sp", opt_ept_exec_sp);
>>>>>>>>>>
>>>>>>>>>> I agree for this one - if the value is still -1, it has neither
>>>>>>>>>> been set nor is its value of any interest.
>>>>>>>>
>>>>>>>> ... here.
>>>>>>>
>>>>>>> I think we should not mix up specified parameters and effective
>>>>>>> settings. In case an effective setting is of common interest it should
>>>>>>> be reported via a specific node (like e.g. specific mitigation settings
>>>>>>> where the cmdline is not providing enough details).
>>>>>>
>>>>>> But then a boolean option that wasn't specified on the command line
>>>>>> should produce no output at all. And hence we'd need a way to tell
>>>>>> whether an option was set from command line for _all_ of them. I
>>>>>> don't think this would be very helpful.
>>>>>
>>>>> I disagree here.
>>>>>
>>>>> This is important only for cases where the hypervisor treats the
>>>>> parameter as a tristate: true/false/unspecified. In all cases where
>>>>> the bool value is really true or false it can be reported as such.
>>>>
>>>> The problem I'm having with this is the resulting inconsistency:
>>>> When we write the variable with 0 or 1 in case we find it to be
>>>> -1 after command line parsing, the externally visible effect will
>>>> be different from the case where we leave it to be -1 yet still
>>>> treat it as (pseudo-)boolean. This, however, is an implementation
>>>> detail, while imo the hypfs presentation should not depend on
>>>> such implementation details.
>>>>
>>>>> Reporting 0/1 for e.g. "ad" if opt_ept_ad==-1 would add a latent problem
>>>>> if any other action would be derived from the parameter variable being
>>>>> -1.
>>>>>
>>>>> So either opt_ept_ad should be modified to change it to 0/1 instead of
>>>>> only setting the VCMS flag,
>>>>
>>>> That's what I did suggest.
>>>>
>>>>> or the logic should be kept as is in this
>>>>> patch. IMO changing the setting of opt_ept_ad should be done in another
>>>>> patch if this is really wanted.
>>>>
>>>> And of course I don't mind at all doing so in a prereq patch.
>>>> It's just that the patch here provides a good place _where_ to
>>>> actually do such an adjustment.
>>>
>>> I was thinking of something like this:
>>>
>>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>>> @@ -313,12 +313,12 @@ static int vmx_init_vmcs_config(void)
>>> {
>>> rdmsrl(MSR_IA32_VMX_EPT_VPID_CAP, _vmx_ept_vpid_cap);
>>>
>>> + if ( /* Work around Erratum AVR41 on Avoton processors. */
>>> + boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 0x4d &&
>>> + opt_ept_ad < 0 )
>>> + opt_ept_ad = 0;
>>> if ( !opt_ept_ad )
>>> _vmx_ept_vpid_cap &= ~VMX_EPT_AD_BIT;
>>> - else if ( /* Work around Erratum AVR41 on Avoton processors. */
>>> - boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 0x4d &&
>>> - opt_ept_ad < 0 )
>>> - _vmx_ept_vpid_cap &= ~VMX_EPT_AD_BIT;
>>>
>>> /*
>>> * Additional sanity checking before using EPT:
>>
>> And I was specifically hoping to avoid doing this in a non-__init
>> function.
>
> Should be fairly easy (see attached patch).
Why not put the opt_ept_ad adjustment right into start_vmx(),
just like e.g. the opt_ept_exec_sp gets also done there? Pulling
the setting up of the 'v' key handler risks installing it ahead
of a potential future later error exit from start_vmx(). But I'm
not entirely opposed to the chosen approach either - it'll be up
to Kevin to judge, I guess.
Jan
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next prev parent reply other threads:[~2020-03-06 9:05 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 12:46 [Xen-devel] [PATCH v6 00/12] Add hypervisor sysfs-like support Juergen Gross
2020-02-26 12:46 ` [Xen-devel] [PATCH v6 01/12] xen: allow only sizeof(bool) variables for boolean_param() Juergen Gross
2020-03-03 16:40 ` Jan Beulich
2020-03-09 11:43 ` Julien Grall
2020-03-09 11:55 ` Jan Beulich
2020-03-09 13:01 ` Jürgen Groß
2020-03-09 13:06 ` Jan Beulich
2020-03-09 14:06 ` Jürgen Groß
2020-02-26 12:46 ` [Xen-devel] [PATCH v6 02/12] xen: add a generic way to include binary files as variables Juergen Gross
2020-02-26 12:46 ` [Xen-devel] [PATCH v6 03/12] docs: add feature document for Xen hypervisor sysfs-like support Juergen Gross
2020-03-09 11:48 ` Julien Grall
2020-03-25 14:05 ` Jürgen Groß
2020-02-26 12:46 ` [Xen-devel] [PATCH v6 04/12] xen: add basic hypervisor filesystem support Juergen Gross
2020-03-03 16:59 ` Jan Beulich
2020-03-04 12:00 ` Jürgen Groß
2020-03-04 13:03 ` Jan Beulich
2020-03-04 14:39 ` Jürgen Groß
2020-03-04 15:07 ` Jan Beulich
2020-03-04 15:14 ` Jürgen Groß
2020-03-04 15:21 ` Jan Beulich
2020-03-06 6:06 ` Jürgen Groß
2020-03-06 8:19 ` Jan Beulich
2020-02-26 12:46 ` [Xen-devel] [PATCH v6 05/12] libs: add libxenhypfs Juergen Gross
2020-02-26 12:46 ` [Xen-devel] [PATCH v6 06/12] tools: add xenfs tool Juergen Gross
2020-02-26 12:47 ` [Xen-devel] [PATCH v6 07/12] xen: provide version information in hypfs Juergen Gross
2020-02-26 12:47 ` [Xen-devel] [PATCH v6 08/12] xen: add /buildinfo/config entry to hypervisor filesystem Juergen Gross
2020-03-04 10:49 ` Jan Beulich
2020-03-04 12:06 ` Jürgen Groß
2020-03-04 13:04 ` Jan Beulich
2020-02-26 12:47 ` [Xen-devel] [PATCH v6 09/12] xen: add runtime parameter access support to hypfs Juergen Gross
2020-03-04 11:32 ` Jan Beulich
2020-03-04 15:07 ` Jürgen Groß
2020-03-04 15:19 ` Jan Beulich
2020-03-04 16:31 ` Jürgen Groß
2020-03-04 16:56 ` Jan Beulich
2020-03-05 6:01 ` Jürgen Groß
2020-03-05 8:26 ` Jan Beulich
2020-03-06 6:42 ` Jürgen Groß
2020-03-06 8:20 ` Jan Beulich
2020-03-06 8:47 ` Jürgen Groß
2020-03-06 9:04 ` Jan Beulich [this message]
2020-03-06 9:20 ` Jürgen Groß
2020-03-06 9:22 ` Jan Beulich
2020-03-06 9:27 ` Jürgen Groß
2020-03-23 10:38 ` Julien Grall
2020-02-26 12:47 ` [Xen-devel] [PATCH v6 10/12] tools/libxl: use libxenhypfs for setting xen runtime parameters Juergen Gross
2020-02-26 12:47 ` [Xen-devel] [PATCH v6 11/12] tools/libxc: remove xc_set_parameters() Juergen Gross
2020-02-26 12:47 ` [Xen-devel] [PATCH v6 12/12] xen: remove XEN_SYSCTL_set_parameter support Juergen Gross
2020-03-04 11:45 ` Jan Beulich
2020-03-04 14:40 ` Jürgen Groß
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