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Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Gonda , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Borislav Petkov , Michael Roth , Vlastimil Babka , tony.luck@intel.com, npmccallum@redhat.com, brijesh.ksingh@gmail.com Subject: Re: [PATCH Part2 RFC v4 01/40] KVM: SVM: Add support to handle AP reset MSR protocol Message-ID: References: <20210707183616.5620-1-brijesh.singh@amd.com> <20210707183616.5620-2-brijesh.singh@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=Twb6x088; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=iCqY9l43; spf=pass (imf17.hostedemail.com: domain of jroedel@suse.de designates 195.135.220.28 as permitted sender) smtp.mailfrom=jroedel@suse.de; dmarc=none X-Rspamd-Server: rspam02 X-Stat-Signature: udyddtayd5zd3ax5q41833czwobetc1p X-Rspamd-Queue-Id: 18EEFF00038D X-HE-Tag: 1626334802-346367 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 14, 2021 at 08:17:29PM +0000, Sean Christopherson wrote: > On Wed, Jul 07, 2021, Brijesh Singh wrote: > > From: Tom Lendacky > > > > Add support for AP Reset Hold being invoked using the GHCB MSR protocol, > > available in version 2 of the GHCB specification. > > Please provide a brief overview of the protocol, and why it's needed. I assume > it's to allow AP wakeup without a shared GHCB? Yes, this is needed for SEV-ES kexec support to park APs without the need for memory that will be owned by the new kernel when APs are woken up. You can have a look into my SEV-ES kexec/kdump patch-set for details: https://lore.kernel.org/lkml/20210705082443.14721-1-joro@8bytes.org/ I also sent this patch separatly earlier this week to enable GHCB protocol version 2 support in KVM. Regards, Joerg