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[192.55.52.115]) by mx.google.com with ESMTPS id w8si3173335pgr.258.2019.06.14.11.42.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Jun 2019 11:42:55 -0700 (PDT) Received-SPF: pass (google.com: domain of alison.schofield@intel.com designates 192.55.52.115 as permitted sender) client-ip=192.55.52.115; Authentication-Results: mx.google.com; spf=pass (google.com: domain of alison.schofield@intel.com designates 192.55.52.115 as permitted sender) smtp.mailfrom=alison.schofield@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jun 2019 11:42:54 -0700 Received: from alison-desk.jf.intel.com ([10.54.74.53]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jun 2019 11:42:55 -0700 Date: Fri, 14 Jun 2019 11:46:02 -0700 From: Alison Schofield To: Dave Hansen Cc: Peter Zijlstra , "Kirill A. Shutemov" , Andrew Morton , x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov , Andy Lutomirski , David Howells , Kees Cook , Kai Huang , Jacob Pan , linux-mm@kvack.org, kvm@vger.kernel.org, keyrings@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH, RFC 44/62] x86/mm: Set KeyIDs in encrypted VMAs for MKTME Message-ID: <20190614184602.GB7252@alison-desk.jf.intel.com> References: <20190508144422.13171-1-kirill.shutemov@linux.intel.com> <20190508144422.13171-45-kirill.shutemov@linux.intel.com> <20190614114408.GD3436@hirez.programming.kicks-ass.net> <20190614173345.GB5917@alison-desk.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) 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 Fri, Jun 14, 2019 at 11:26:10AM -0700, Dave Hansen wrote: > On 6/14/19 10:33 AM, Alison Schofield wrote: > > Preserving the data across encryption key changes has not > > been a requirement. I'm not clear if it was ever considered > > and rejected. I believe that copying in order to preserve > > the data was never considered. > > We could preserve the data pretty easily. It's just annoying, though. > Right now, our only KeyID conversions happen in the page allocator. If > we were to convert in-place, we'd need something along the lines of: > > 1. Allocate a scratch page > 2. Unmap target page, or at least make it entirely read-only > 3. Copy plaintext into scratch page > 4. Do cache KeyID conversion of page being converted: > Flush caches, change page_ext metadata > 5. Copy plaintext back into target page from scratch area > 6. Re-establish PTEs with new KeyID Seems like the 'Copy plaintext' steps might disappoint the user, as much as the 'we don't preserve your data' design. Would users be happy w the plain text steps ? Alison > > #2 is *really* hard. It's similar to the problems that the poor > filesystem guys are having with RDMA these days when RDMA is doing writes. > > What we have here (destroying existing data) is certainly the _simplest_ > semantic. We can certainly give it a different name, or even non-PROT_* > semantics where it shares none of mprotect()'s functionality. > > Doesn't really matter to me at all.