From: Ashish Kalra <ashish.kalra@amd.com>
To: Steve Rutherford <srutherford@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Singh, Brijesh" <brijesh.singh@amd.com>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@suse.de>,
"Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
X86 ML <x86@kernel.org>, KVM list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"dovmurik@linux.vnet.ibm.com" <dovmurik@linux.vnet.ibm.com>,
"tobin@ibm.com" <tobin@ibm.com>,
"jejb@linux.ibm.com" <jejb@linux.ibm.com>,
"frankeh@us.ibm.com" <frankeh@us.ibm.com>,
jon.grimm@amd.com
Subject: Re: [PATCH v2 1/9] KVM: x86: Add AMD SEV specific Hypercall3
Date: Fri, 8 Jan 2021 00:47:56 +0000 [thread overview]
Message-ID: <20210108004756.GA17895@ashkalra_ubuntu_server> (raw)
In-Reply-To: <20210107080513.GA16781@ashkalra_ubuntu_server>
> On Thu, Jan 07, 2021 at 01:34:14AM +0000, Ashish Kalra wrote:
> > Hello Steve,
> >
> > My thoughts here ...
> >
> > On Wed, Jan 06, 2021 at 05:01:33PM -0800, Steve Rutherford wrote:
> > > Avoiding an rbtree for such a small (but unstable) list seems correct.
> > >
> >
> > I agree.
> >
> > > For the unencrypted region list strategy, the only questions that I
> > > have are fairly secondary.
> > > - How should the kernel upper bound the size of the list in the face
> > > of malicious guests, but still support large guests? (Something
> > > similar to the size provided in the bitmap API would work).
> > > - What serialization format should be used for the ioctl API?
> > > (Usermode could send down a pointer to a user region and a size. The
> > > kernel could then populate that with an array of structs containing
> > > bases and limits for unencrypted regions.)
> > > - How will the kernel tag a guest as having exceeded its maximum list
> > > size, in order to indicate that the list is now incomplete? (Track a
> > > poison bit, and send it up when getting the serialized list of
> > > regions).
> > >
> > > In my view, there are two main competitors to this strategy:
> > > - (Existing) Bitmap API
> > > - A guest memory donation based model
> > >
> > > The existing bitmap API avoids any issues with growing too large,
> > > since it's size is predictable.
> > >
> > > To elaborate on the memory donation based model, the guest could put
> > > an encryption status data structure into unencrypted guest memory, and
> > > then use a hypercall to inform the host where the base of that
> > > structure is located. The main advantage of this is that it side steps
> > > any issues around malicious guests causing large allocations.
> > >
> > > The unencrypted region list seems very practical. It's biggest
> > > advantage over the bitmap is how cheap it will be to pass the
> > > structure up from the kernel. A memory donation based model could
> > > achieve similar performance, but with some additional complexity.
> > >
> > > Does anyone view the memory donation model as worth the complexity?
> > > Does anyone think the simplicity of the bitmap is a better tradeoff
> > > compared to an unencrypted region list?
> >
> > One advantage in sticking with the bitmap is that it maps very nicely to
> > the dirty bitmap page tracking logic in KVM/Qemu. The way Brijesh
> > designed and implemented it is very similar to dirty page bitmap tracking
> > and syncing between KVM and Qemu. The same logic is re-used for the page
> > encryption bitmap which means quite mininal changes and code resuse in
> > Qemu.
> >
> > Any changes to the backing data structure, will require additional
> > mapping logic to be added to Qemu.
> >
> > This is one advantage in keeping the bitmap logic.
> >
So if nobody is in favor of keeping the (current) bitmap logic, we will
move to the unencrypted region list approach.
Thanks,
Ashish
next prev parent reply other threads:[~2021-01-08 0:48 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 0:45 [PATCH v2 0/9] Add AMD SEV page encryption bitmap support Ashish Kalra
2020-12-01 0:45 ` [PATCH v2 1/9] KVM: x86: Add AMD SEV specific Hypercall3 Ashish Kalra
2020-12-03 0:34 ` Sean Christopherson
2020-12-04 17:16 ` Brijesh Singh
2020-12-06 10:26 ` Paolo Bonzini
2020-12-07 20:41 ` Sean Christopherson
2020-12-08 3:09 ` Steve Rutherford
2020-12-08 4:16 ` Kalra, Ashish
2020-12-08 16:29 ` Brijesh Singh
2020-12-11 22:55 ` Ashish Kalra
2020-12-12 4:56 ` Ashish Kalra
2020-12-18 19:39 ` Dr. David Alan Gilbert
[not found] ` <E79E09A2-F314-4B59-B7AE-07B1D422DF2B@amd.com>
2020-12-18 19:56 ` Dr. David Alan Gilbert
2021-01-06 23:05 ` Ashish Kalra
2021-01-07 1:01 ` Steve Rutherford
2021-01-07 1:34 ` Ashish Kalra
2021-01-07 8:05 ` Ashish Kalra
2021-01-08 0:47 ` Ashish Kalra [this message]
2021-01-08 0:55 ` Steve Rutherford
2021-01-07 17:07 ` Ashish Kalra
2021-01-07 17:26 ` Sean Christopherson
2021-01-07 18:41 ` Ashish Kalra
2021-01-07 19:22 ` Sean Christopherson
2021-01-08 0:54 ` Steve Rutherford
2021-01-08 16:56 ` Sean Christopherson
2020-12-01 0:46 ` [PATCH v2 2/9] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall Ashish Kalra
2020-12-02 16:54 ` Dr. David Alan Gilbert
2020-12-02 21:22 ` Ashish Kalra
2020-12-06 10:25 ` Paolo Bonzini
2020-12-01 0:47 ` [PATCH v2 3/9] KVM: x86: Introduce KVM_GET_PAGE_ENC_BITMAP ioctl Ashish Kalra
2020-12-06 11:02 ` Dov Murik
2020-12-07 22:00 ` Ashish Kalra
2020-12-01 0:47 ` [PATCH v2 4/9] mm: x86: Invoke hypercall when page encryption status is changed Ashish Kalra
2020-12-01 0:47 ` [PATCH v2 5/9] KVM: x86: Introduce KVM_SET_PAGE_ENC_BITMAP ioctl Ashish Kalra
2020-12-01 0:47 ` [PATCH v2 6/9] KVM: SVM: Add support for static allocation of unified Page Encryption Bitmap Ashish Kalra
2020-12-01 0:48 ` [PATCH v2 7/9] KVM: x86: Mark _bss_decrypted section variables as decrypted in page encryption bitmap Ashish Kalra
2020-12-01 0:48 ` [PATCH v2 8/9] KVM: x86: Add kexec support for SEV " Ashish Kalra
2020-12-01 0:48 ` [PATCH v2 9/9] KVM: SVM: Bypass DBG_DECRYPT API calls for unecrypted guest memory Ashish Kalra
2020-12-08 5:18 [PATCH v2 1/9] KVM: x86: Add AMD SEV specific Hypercall3 Kalra, Ashish
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210108004756.GA17895@ashkalra_ubuntu_server \
--to=ashish.kalra@amd.com \
--cc=Thomas.Lendacky@amd.com \
--cc=bp@suse.de \
--cc=brijesh.singh@amd.com \
--cc=dgilbert@redhat.com \
--cc=dovmurik@linux.vnet.ibm.com \
--cc=frankeh@us.ibm.com \
--cc=hpa@zytor.com \
--cc=jejb@linux.ibm.com \
--cc=jon.grimm@amd.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=srutherford@google.com \
--cc=tglx@linutronix.de \
--cc=tobin@ibm.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).