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Message-ID: <fed13d3d-c87c-4e5c-9451-779200c35a1c@suse.com>
Date: Mon, 29 Jan 2024 09:22:13 +0200
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Subject: Re: [PATCHv6 09/16] x86/mm: Adding callbacks to prepare encrypted
 memory for kexec
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
 Peter Zijlstra <peterz@infradead.org>,
 Adrian Hunter <adrian.hunter@intel.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
 Elena Reshetova <elena.reshetova@intel.com>,
 Jun Nakajima <jun.nakajima@intel.com>,
 Rick Edgecombe <rick.p.edgecombe@intel.com>,
 Tom Lendacky <thomas.lendacky@amd.com>, "Kalra, Ashish"
 <ashish.kalra@amd.com>, Sean Christopherson <seanjc@google.com>,
 "Huang, Kai" <kai.huang@intel.com>, Baoquan He <bhe@redhat.com>,
 kexec@lists.infradead.org, linux-coco@lists.linux.dev,
 linux-kernel@vger.kernel.org
References: <20240124125557.493675-1-kirill.shutemov@linux.intel.com>
 <20240124125557.493675-10-kirill.shutemov@linux.intel.com>
From: Nikolay Borisov <nik.borisov@suse.com>
In-Reply-To: <20240124125557.493675-10-kirill.shutemov@linux.intel.com>
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On 24.01.24 г. 14:55 ч., 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@linux.intel.com>

Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>