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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>, "X86 ML" <x86@kernel.org>,
	"Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"kvm list" <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-sgx@vger.kernel.org
Subject: Re: [RFC PATCH 04/21] x86/sgx: Add /dev/sgx/virt_epc device to allocate "raw" EPC for VMs
Date: Mon, 29 Jul 2019 10:05:47 -0700
Message-ID: <20190729170547.GH21120@linux.intel.com> (raw)
In-Reply-To: <CALCETrXLE6RpR9p9eGPNvU+Nt=yyCkqsQHv7hzmNaC61sFK7Jg@mail.gmail.com>

On Sat, Jul 27, 2019 at 10:44:24AM -0700, Andy Lutomirski wrote:
> On Fri, Jul 26, 2019 at 10:52 PM Sean Christopherson
> <sean.j.christopherson@intel.com> wrote:
> >
> > Add an SGX device to enable userspace to allocate EPC without an
> > associated enclave.  The intended and only known use case for direct EPC
> > allocation is to expose EPC to a KVM guest, hence the virt_epc moniker,
> > virt.{c,h} files and INTEL_SGX_VIRTUALIZATION Kconfig.
> >
> > Although KVM is the end consumer of EPC, and will need hooks into the
> > virtual EPC management if oversubscription of EPC for guest is ever
> > supported (see below), implement direct access to EPC in the SGX
> > subsystem instead of in KVM.  Doing so has two major advantages:
> >
> >   - Does not require changes to KVM's uAPI, e.g. EPC gets handled as
> >     just another memory backend for guests.
> 
> This is general grumbling more than useful feedback, but I wish there
> was a way for KVM's userspace to add a memory region that is *not*
> backed by a memory mapping.  For SGX, this would avoid the slightly
> awkward situation where useless EPC pages are mapped by QEMU.  For
> SEV, it would solve the really fairly awful situation where the SEV
> pages are mapped *incoherently* for QEMU.  And even in the absence of
> fancy hardware features, it would allow the guest to have secrets in
> memory that are not exposed to wild reads, speculation attacks, etc
> coming from QEMU.
> 
> I realize the implementation would be extremely intrusive, but it just
> might make it a lot easier to do things like making SEV pages property
> movable.  Similarly, I could see EPC oversubscription being less nasty
> in this model.  For one thing, it would make it more straightforward
> to keep track of exactly which VMs have a given EPC page mapped,
> whereas right now this driver only really knows which host userspace
> mm has the EPC page mapped.

Host userspace vs VM doesn't add much, if any, complexity to EPC
oversubscription, especially since the problem of supporting multiple mm
structs needs to be solved for the native driver anyways.

The nastiness of oversubscribing a VM is primarily in dealing with
EBLOCK/ETRACK/EWB conflicts between guest and host.  The other nasty bit
is that it all but requires fancier VA page management, e.g. allocating a
dedicated VA slot for every EPC page doesn't scale when presenting a
multi-{GB,TB} EPC to a guest, especially since there's no guarantee the
guest will ever access EPC.

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-27  5:51 [RFC PATCH 00/21] x86/sgx: KVM: Add SGX virtualization Sean Christopherson
2019-07-27  5:51 ` [RFC PATCH 01/21] x86/sgx: Add defines for SGX device minor numbers Sean Christopherson
2019-07-27  5:51 ` [RFC PATCH 02/21] x86/sgx: Move bus registration and device init to common code Sean Christopherson
2019-07-27  5:51 ` [RFC PATCH 03/21] x86/sgx: Move provisioning device " Sean Christopherson
2019-07-27  5:51 ` [RFC PATCH 04/21] x86/sgx: Add /dev/sgx/virt_epc device to allocate "raw" EPC for VMs Sean Christopherson
2019-07-27 17:44   ` Andy Lutomirski
2019-07-29 17:05     ` Sean Christopherson [this message]
2019-07-27  5:51 ` [RFC PATCH 05/21] x86/sgx: Expose SGX architectural definitions to the kernel Sean Christopherson
2019-07-27  5:51 ` [RFC PATCH 06/21] KVM: x86: Add SGX sub-features leaf to reverse CPUID table Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 07/21] KVM: x86: Add WARN_ON_ONCE(index!=0) in __do_cpuid_ent Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 08/21] KVM: x86: Add kvm_x86_ops hook to short circuit emulation Sean Christopherson
2019-07-27 17:38   ` Andy Lutomirski
2019-07-30  2:49     ` Sean Christopherson
2019-08-16  0:47       ` Andy Lutomirski
2019-08-19 22:01         ` Sean Christopherson
2019-08-20  1:34           ` Andy Lutomirski
2019-08-20  1:41             ` Sean Christopherson
2019-07-30  3:08   ` Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 09/21] KVM: VMX: Add basic handling of VM-Exit from SGX enclave Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 10/21] KVM: x86: Export kvm_mmu_gva_to_gpa_{read,write}() for VMX/SGX Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 11/21] KVM: x86: Export kvm_propagate_fault (as kvm_propagate_page_fault) Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 12/21] KVM: x86: Define new #PF SGX error code bit Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 13/21] x86/sgx: Move the intermediate EINIT helper into the driver Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 14/21] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 15/21] KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 16/21] KVM: VMX: Edd emulation of SGX Launch Control LE hash MSRs Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 17/21] KVM: VMX: Add handler for ENCLS[EINIT] to support SGX Launch Control Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 18/21] KVM: x86: Invoke kvm_x86_ops->cpuid_update() after kvm_update_cpuid() Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 19/21] KVM: VMX: Enable SGX virtualization for SGX1, SGX2 and LC Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 20/21] x86/sgx: Export sgx_set_attribute() for use by KVM Sean Christopherson
2019-07-27  5:52 ` [RFC PATCH 21/21] KVM: x86: Add capability to grant VM access to privileged SGX attribute Sean Christopherson
2019-07-27 17:32   ` Andy Lutomirski

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