From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E69332C9E for ; Mon, 27 Jun 2022 11:30:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1656329422; x=1687865422; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=O/C94ZB/s6G9BRryYo+Qz3Y2uZ2+Yo0+K1mSVtuIqz8=; b=GoQhvd/vnnanULk14E/nPoQuQfmKn2BvtLFPVhVvjQUgraW+S9ZYDILp fTloZ6l8TsVywLZPmSEnmhUR9TK3VLDWKFlXPWUiaBVXVf2wVsKfmkAC7 MArFRZoIx/MH4lHt/+dOEbJhcyqCbXRziWTnKd+UdMJ2/mkhSna3iRrVI Ai1KUJ3Qxp6Ld6RRw3Oz8shlhQDL5AGCQwKbagAnAsXCBiZrPhPZjjZN5 lq5sCDY+kKPpLAQO12XccJD+5rINYoZDpvoHH8uuYCgrjdcl1U9bz0e5Q TZeaQLdZekXGQpEfeV9yDn5kzWp9LP6dW+1stsoaLZlAd+JTkEkWoGrq7 g==; X-IronPort-AV: E=McAfee;i="6400,9594,10390"; a="306902244" X-IronPort-AV: E=Sophos;i="5.92,226,1650956400"; d="scan'208";a="306902244" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Jun 2022 04:30:22 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.92,226,1650956400"; d="scan'208";a="916678660" Received: from black.fi.intel.com ([10.237.72.28]) by fmsmga005.fm.intel.com with ESMTP; 27 Jun 2022 04:30:14 -0700 Received: by black.fi.intel.com (Postfix, from userid 1000) id 1C5F7D9; Mon, 27 Jun 2022 14:30:19 +0300 (EEST) Date: Mon, 27 Jun 2022 14:30:19 +0300 From: "Kirill A. Shutemov" To: Peter Gonda Cc: Borislav Petkov , Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel , Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Varad Gautam , Dario Faggioli , Dave Hansen , Mike Rapoport , David Hildenbrand , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, the arch/x86 maintainers , linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, LKML Subject: Re: [PATCHv7 00/14] mm, x86/cc: Implement support for unaccepted memory Message-ID: <20220627113019.3q62luiay7izhehr@black.fi.intel.com> References: <20220614120231.48165-1-kirill.shutemov@linux.intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jun 24, 2022 at 10:37:10AM -0600, Peter Gonda wrote: > On Tue, Jun 14, 2022 at 6:03 AM Kirill A. Shutemov > wrote: > > > > UEFI Specification version 2.9 introduces the concept of memory > > acceptance: some Virtual Machine platforms, such as Intel TDX or AMD > > SEV-SNP, requiring memory to be accepted before it can be used by the > > guest. Accepting happens via a protocol specific for the Virtual > > Machine platform. > > > > Accepting memory is costly and it makes VMM allocate memory for the > > accepted guest physical address range. It's better to postpone memory > > acceptance until memory is needed. It lowers boot time and reduces > > memory overhead. > > > > The kernel needs to know what memory has been accepted. Firmware > > communicates this information via memory map: a new memory type -- > > EFI_UNACCEPTED_MEMORY -- indicates such memory. > > > > Range-based tracking works fine for firmware, but it gets bulky for > > the kernel: e820 has to be modified on every page acceptance. It leads > > to table fragmentation, but there's a limited number of entries in the > > e820 table > > > > Another option is to mark such memory as usable in e820 and track if the > > range has been accepted in a bitmap. One bit in the bitmap represents > > 2MiB in the address space: one 4k page is enough to track 64GiB or > > physical address space. > > > > In the worst-case scenario -- a huge hole in the middle of the > > address space -- It needs 256MiB to handle 4PiB of the address > > space. > > > > Any unaccepted memory that is not aligned to 2M gets accepted upfront. > > > > The approach lowers boot time substantially. Boot to shell is ~2.5x > > faster for 4G TDX VM and ~4x faster for 64G. > > > > TDX-specific code isolated from the core of unaccepted memory support. It > > supposed to help to plug-in different implementation of unaccepted memory > > such as SEV-SNP. > > > > The tree can be found here: > > > > https://github.com/intel/tdx.git guest-unaccepted-memory > > Hi Kirill, > > I have a couple questions about this feature mainly about how cloud > customers can use this, I assume since this is a confidential compute > feature a large number of the users of these patches will be cloud > customers using TDX and SNP. One issue I see with these patches is how > do we as a cloud provider know whether a customer's linux image > supports this feature, if the image doesn't have these patches UEFI > needs to fully validate the memory, if the image does we can use this > new protocol. In GCE we supply our VMs with a version of the EDK2 FW > and the customer doesn't input into which UEFI we run, as far as I can > tell from the Azure SNP VM documentation it seems very similar. We > need to somehow tell our UEFI in the VM what to do based on the image. > The current way I can see to solve this issue would be to have our > customers give us metadata about their VM's image but this seems kinda > burdensome on our customers (I assume we'll have more features which > both UEFI and kernel need to both support inorder to be turned on like > this one) and error-prone, if a customer incorrectly labels their > image it may fail to boot.. Has there been any discussion about how to > solve this? My naive thoughts were what if UEFI and Kernel had some > sort of feature negotiation. Maybe that could happen via an extension > to exit boot services or a UEFI runtime driver, I'm not sure what's > best here just some ideas. Just as an idea, we can put info into UTS_VERSION which can be read from the built bzImage. We have info on SMP and preeption there already. Patch below does this: $ file arch/x86/boot/bzImage arch/x86/boot/bzImage: Linux kernel x86 boot executable bzImage, version 5.19.0-rc3-00016-g2f6aa48e28d9-dirty (kas@box) #2300 SMP PREEMPT_DYNAMIC UNACCEPTED_MEMORY Mon Jun 27 14:23:04 , RO-rootFS, swap_dev 0XC, Normal VGA Note UNACCEPTED_MEMORY in the output. Probably we want to have there info on which flavour of unaccepted memory is supported (TDX/SNP/whatever). It is a bit more tricky. Any opinion? diff --git a/init/Makefile b/init/Makefile index d82623d7fc8e..6688ea43e6bf 100644 --- a/init/Makefile +++ b/init/Makefile @@ -32,7 +32,7 @@ quiet_cmd_compile.h = CHK $@ $(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@ \ "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT_BUILD)" \ "$(CONFIG_PREEMPT_DYNAMIC)" "$(CONFIG_PREEMPT_RT)" \ - "$(CONFIG_CC_VERSION_TEXT)" "$(LD)" + "$(CONFIG_UNACCEPTED_MEMORY)" "$(CONFIG_CC_VERSION_TEXT)" "$(LD)" include/generated/compile.h: FORCE $(call cmd,compile.h) diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h index ca40a5258c87..efacfecad699 100755 --- a/scripts/mkcompile_h +++ b/scripts/mkcompile_h @@ -7,8 +7,9 @@ SMP=$3 PREEMPT=$4 PREEMPT_DYNAMIC=$5 PREEMPT_RT=$6 -CC_VERSION="$7" -LD=$8 +UNACCEPTED_MEMORY=$7 +CC_VERSION="$8" +LD=$9 # Do not expand names set -f @@ -51,6 +52,10 @@ elif [ -n "$PREEMPT" ] ; then CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT" fi +if [ -n "$UNACCEPTED_MEMORY" ] ; then + CONFIG_FLAGS="$CONFIG_FLAGS UNACCEPTED_MEMORY" +fi + # Truncate to maximum length UTS_LEN=64 UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)" -- Kirill A. Shutemov