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Message-ID: <PH7PR11MB8455BCD71320C0C081C29AEB9A832@PH7PR11MB8455.namprd11.prod.outlook.com>
Date: Wed, 30 Apr 2025 11:10:32 +0000
From: "Miao, Jun" <jun.miao@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, "Li, Zhiquan1"
<zhiquan1.li@...el.com>
CC: "Hansen, Dave" <dave.hansen@...el.com>, "dave.hansen@...ux.intel.com"
<dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>,
"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
<mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>, "Du, Fan"
<fan.du@...el.com>, "Miao, Jun" <jun.miao@...el.com>
Subject: RE: [V2 PATCH] x86/tdx: add VIRT_CPUID2 virtualization if REDUCE_VE
was not successful
>
>On Wed, Apr 30, 2025 at 10:15:05AM +0800, Zhiquan Li wrote:
>>
>> On 2025/4/29 22:50, Dave Hansen wrote:
>> > On 4/29/25 07:31, Jun Miao wrote:
>> >> REDUCE_VE can only be enabled if x2APIC_ID has been properly
>> >> configured with unique values for each VCPU. Check if VMM has
>> >> provided an activated topology configuration first as it is the
>> >> prerequisite of REDUCE_VE and ENUM_TOPOLOGY, so move it to
>> >> reduce_unnecessary_ve(). The function
>> >> enable_cpu_topology_enumeration() was very little and can be
>> >> integrated into reduce_unnecessary_ve().
>> >
>> > Isn't this just working around VMM bugs? Shouldn't we just panic as
>> > quickly as possible so the VMM config gets fixed rather than adding kludges?
>>
>>
>> Now failed to virtualize these two cases will cause TD VM regression
>> vs legacy VM. Do you mean the panic will just for the #VE caused by
>> CPUID leaf 0x2? Or both (+ VMM not configure topology) will panic?
>>
>> Currently the most customer's complaints come from the CPUID leaf 0x2
>> not virtualization, and most of access come from user space. Is it
>> appropriate for such behavior directly cause a guest kernel panic?
>
>The appropriate behavior would be to fix VMM to configure APIC IDs correctly and
>use TDX module that supports REDUCE_VE.
>
Yes, I completely agree with your point to fix VMM APIC IDs.
The idea here is only to avoid this panic by using the guest component even when the host is incomplete.
And thereby improving the robustness of the kernel code. Moreover, even if the VMM becomes complete later, the adjusted logic will continue to adapt still. (^v^)
--- Jun Miao
>--
> Kiryl Shutsemau / Kirill A. Shutemov
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