linux-kernel - Re: [PATCH v2 2/5] x86/kexec: do unconditional WBINVD in relocate

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Message-ID: <689bbd29-aaf0-452e-a97f-41b8e3aa6224@intel.com>
Date: Wed, 20 Mar 2024 10:20:50 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: Tom Lendacky <thomas.lendacky@....com>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>
CC: <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <dave.hansen@...el.com>,
	<bp@...en8.de>, <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
	<luto@...nel.org>, <peterz@...radead.org>, <rick.p.edgecombe@...el.com>,
	<ashish.kalra@....com>, <chao.gao@...el.com>, <bhe@...hat.com>,
	<nik.borisov@...e.com>, <pbonzini@...hat.com>, <seanjc@...gle.com>
Subject: Re: [PATCH v2 2/5] x86/kexec: do unconditional WBINVD in
 relocate_kernel()



On 20/03/2024 3:38 am, Tom Lendacky wrote:
> On 3/19/24 06:13, Kirill A. Shutemov wrote:
>> On Tue, Mar 19, 2024 at 01:48:45AM +0000, Kai Huang wrote:
>>> Both SME and TDX can leave caches in incoherent state due to memory
>>> encryption.  During kexec, the caches must be flushed before jumping to
>>> the second kernel to avoid silent memory corruption to the second 
>>> kernel.
>>>
>>> During kexec, the WBINVD in stop_this_cpu() flushes caches for all
>>> remote cpus when they are being stopped.  For SME, the WBINVD in
>>> relocate_kernel() flushes the cache for the last running cpu (which is
>>> executing the kexec).
>>>
>>> Similarly, for TDX after stopping all remote cpus with cache flushed, to
>>> support kexec, the kernel needs to flush cache for the last running cpu.
>>>
>>> Make the WBINVD in the relocate_kernel() unconditional to cover both SME
>>> and TDX.
>>
>> Nope. It breaks TDX guest. WBINVD triggers #VE for TDX guests.
> 
> Ditto for SEV-ES/SEV-SNP, a #VC is generated and crashes the guest.
> 

Oh I forgot these.

Hi Kirill,

Then I think patch 1 will also break TDX guest after your series to 
enable multiple cpus for the second kernel after kexec()?

Hi Tom,

I am not aware of kexec() support status for SEV-ES/SEV-SNP guests. 
Does patch 1 break them?