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

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Message-ID: <38fca2fa-11b2-4eb7-9e59-dc5d524d172e@amd.com>
Date: Tue, 19 Mar 2024 09:38:30 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Kai Huang <kai.huang@...el.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 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.

Thanks,
Tom

>