linux-kernel - Re: [PATCHv9 09/17] x86/mm: Adding callbacks to prepare encrypted memory for kexec

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Date: Thu, 4 Apr 2024 11:33:30 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>
CC: "Rafael J. Wysocki" <rafael@...nel.org>, Peter Zijlstra
	<peterz@...radead.org>, Adrian Hunter <adrian.hunter@...el.com>, "Kuppuswamy
 Sathyanarayanan" <sathyanarayanan.kuppuswamy@...ux.intel.com>, Elena
 Reshetova <elena.reshetova@...el.com>, Jun Nakajima <jun.nakajima@...el.com>,
	"Rick Edgecombe" <rick.p.edgecombe@...el.com>, Tom Lendacky
	<thomas.lendacky@....com>, "Kalra, Ashish" <ashish.kalra@....com>, "Sean
 Christopherson" <seanjc@...gle.com>, Baoquan He <bhe@...hat.com>,
	<kexec@...ts.infradead.org>, <linux-coco@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, Nikolay Borisov <nik.borisov@...e.com>
Subject: Re: [PATCHv9 09/17] x86/mm: Adding callbacks to prepare encrypted
 memory for kexec



On 25/03/2024 11:39 pm, Kirill A. Shutemov wrote:
> AMD SEV and Intel TDX guests allocate shared buffers for performing I/O.
> This is done by allocating pages normally from the buddy allocator and
> then converting them to shared using set_memory_decrypted().
> 
> On kexec, the second kernel is unaware of which memory has been
> converted in this manner. It only sees E820_TYPE_RAM. Accessing shared
> memory as private is fatal.
> 
> Therefore, the memory state must be reset to its original state before
> starting the new kernel with kexec.
> 
> The process of converting shared memory back to private occurs in two
> steps:
> 
> - enc_kexec_stop_conversion() stops new conversions.
> 
> - enc_kexec_unshare_mem() unshares all existing shared memory, reverting
>    it back to private.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>x
> ---

Reviewed-by: Kai Huang <kai.huang@...el.com>