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

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Date: Wed, 20 Mar 2024 10:08:09 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: Borislav Petkov <bp@...en8.de>
CC: <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <dave.hansen@...el.com>,
	<kirill.shutemov@...ux.intel.com>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<hpa@...or.com>, <luto@...nel.org>, <peterz@...radead.org>,
	<rick.p.edgecombe@...el.com>, <thomas.lendacky@....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 4:41 am, Borislav Petkov 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.
>>
>> Signed-off-by: Kai Huang <kai.huang@...el.com>
>> Suggested-by: Borislav Petkov <bp@...en8.de>
> 
> Well, I suggested what you have in patch 1 but not this.
> 
> You can't just slap tags willy nilly to patches.
> 

Apologize.  Will remove.