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

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Date: Tue, 19 Mar 2024 13:13:51 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: 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, 
	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 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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov