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Date: Wed, 10 Apr 2024 17:15:11 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Kai Huang <kai.huang@intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, dave.hansen@intel.com, 
	bp@alien8.de, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, 
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	thomas.lendacky@amd.com, ashish.kalra@amd.com, chao.gao@intel.com, bhe@redhat.com, 
	nik.borisov@suse.com, pbonzini@redhat.com, seanjc@google.com
Subject: Re: [PATCH v3 2/5] x86/kexec: do unconditional WBINVD for bare-metal
 in relocate_kernel()
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References: <cover.1712493366.git.kai.huang@intel.com>
 <5aca124fe0ca1c97bf4a2e925b3905485bf5b255.1712493366.git.kai.huang@intel.com>
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In-Reply-To: <5aca124fe0ca1c97bf4a2e925b3905485bf5b255.1712493366.git.kai.huang@intel.com>

On Mon, Apr 08, 2024 at 12:44:55AM +1200, 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, to support kexec for TDX host, after stopping all remote cpus
> with cache flushed, the kernel needs to flush cache for the last running
> cpu.
> 
> Use the existing WBINVD in relocate_kernel() to cover TDX host as well.
> 
> However, instead of sprinkling around vendor-specific checks, just do
> unconditional WBINVD to cover both SME and TDX.  Kexec is not a fast path
> so having one additional WBINVD for platforms w/o SME/TDX is acceptable.
> 
> But only do WBINVD for bare-metal because TDX guests and SEV-ES/SEV-SNP
> guests will get unexpected (and yet unnecessary) #VE which the kernel is
> unable to handle at this stage.
> 
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Dave Young <dyoung@redhat.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov