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dkim=none (message not signed) header.d=none;namei.org; dmarc=none action=none header.from=oracle.com; Received: from BYAPR10MB3077.namprd10.prod.outlook.com (2603:10b6:a03:8c::12) by BY5PR10MB4065.namprd10.prod.outlook.com (2603:10b6:a03:1f6::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3784.12; Fri, 29 Jan 2021 17:22:47 +0000 Received: from BYAPR10MB3077.namprd10.prod.outlook.com ([fe80::74a8:8649:e20b:d571]) by BYAPR10MB3077.namprd10.prod.outlook.com ([fe80::74a8:8649:e20b:d571%7]) with mapi id 15.20.3805.019; Fri, 29 Jan 2021 17:22:47 +0000 Subject: Re: dax alignment problem on arm64 (and other achitectures) To: Pavel Tatashin Cc: Dan Williams , David Hildenbrand , linux-mm , LKML , Sasha Levin , Tyler Hicks , Andrew Morton , Michal Hocko , Oscar Salvador , Vlastimil Babka , Joonsoo Kim , Jason Gunthorpe , Marc Zyngier , Linux ARM , Will Deacon , James Morse , James Morris References: <8c2b75fe-a3e5-8eff-7f37-5d23c7ad9742@redhat.com> From: Joao Martins Message-ID: <43cf3221-1797-dd17-153e-7dda003376ef@oracle.com> Date: Fri, 29 Jan 2021 17:22:38 +0000 In-Reply-To: Content-Type: text/plain; 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So, if >>>> you are willing to maintain the metadata external to the device (which >>>> seems reasonable for your environment) and have your platform firmware >>>> / kernel command line mark it as EFI_CONVENTIONAL_MEMORY + >>>> EFI_MEMORY_SP, then these reserve-free dax-devices will surface. >>> >>> Hi Dan, >>> >>> This is cool. Does it allow conversion between devdax and fsdax so DAX >>> aware filesystem can be installed and data can be put there to be >>> preserved across the reboot? >>> >> >> fwiw wrt to the 'preserved across kexec' part, you are going to need >> something conceptually similar to snippet below the scissors mark. >> Alternatively, we could fix kexec userspace to add conventional memory >> ranges (without the SP attribute part) when it sees a Soft-Reserved region. >> But can't tell which one is the right thing to do. > > Hi Joao, > > Is not it just a matter of appending arguments to the kernel parameter > during kexec reboot with Soft-Reserved region specified, or am I > missing something? I understand with fileload kexec syscall we might > accidently load segments onto reserved region, but with the original > kexec syscall, where we can specify destinations for each segment that > should not be a problem with today's kexec tools. > efi_fake_mem only works with EFI_MEMMAP conventional memory ranges, thus not having a EFI_MEMMAP with RAM ranges means it's a nop for the soft-reserved regions. Unless, you trying to suggest something like: memmap=%+0xefffffff ... To mark soft reserved on top an existing RAM? Sadly don't know if there's an equivalent for ARM. > I agree that preserving it automatically as you are proposing, would > make more sense, instead of fiddling with kernel parameters and > segment destinations. > > Thank you, > Pasha > >> >> At the moment, HMAT ranges (or those defined with efi_fake_mem=) aren't >> preserved not because of anything special with HMAT, but simply because >> the EFI memmap conventional ram ranges are not preserved (only runtime >> services). And HMAT/efi_fake_mem expects these to based on EFI memmap. >> [snip]