From: Jason Gunthorpe <jgg@ziepe.ca>
To: Xu Yilun <yilun.xu@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>,
Ackerley Tng <ackerleytng@google.com>,
Alexey Kardashevskiy <aik@amd.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Kevin Tian <kevin.tian@intel.com>, Joerg Roedel <joro@8bytes.org>,
Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Steve Sistare <steven.sistare@oracle.com>,
Nicolin Chen <nicolinc@nvidia.com>,
iommu@lists.linux.dev, linux-coco@lists.linux.dev,
Dan Williams <dan.j.williams@intel.com>,
Santosh Shukla <santosh.shukla@amd.com>,
"Pratik R . Sampat" <prsampat@amd.com>,
Fuad Tabba <tabba@google.com>,
"Aneesh Kumar K . V" <aneesh.kumar@kernel.org>,
michael.roth@amd.com, vannapurve@google.com
Subject: Re: [RFC PATCH kernel] iommufd: Allow mapping from KVM's guest_memfd
Date: Fri, 27 Feb 2026 09:18:15 -0400 [thread overview]
Message-ID: <20260227131815.GG44359@ziepe.ca> (raw)
In-Reply-To: <aaFzgGTpZI0eZWdD@yilunxu-OptiPlex-7050>
On Fri, Feb 27, 2026 at 06:35:44PM +0800, Xu Yilun wrote:
> Will cause host machine check and host restart, same as host CPU
> accessing encrypted memory. Intel TDX has no lower level privilege
> protection table so the wrong accessing will actually impact the
> memory encryption engine.
Blah, of course it does.
So Intel needs a two step synchronization to wipe the IOPTEs before
any shared private conversions and restore the right ones after.
AMD needs a nasty HW synchronization with RMP changes, but otherwise
wants to map the entire physical space.
ARM doesn't care much, I think it could safely do either approach?
These are very different behaviors so I would expect that userspace
needs to signal which of the two it wants.
It feels like we need a fairly complex dedicated synchronization logic
in iommufd coupled to the shared/private machinery in guestmemfd
Not really sure how to implement the Intel version right now, it is
sort of like a nasty version of SVA..
Jason
next prev parent reply other threads:[~2026-02-27 13:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-25 7:52 [RFC PATCH kernel] iommufd: Allow mapping from KVM's guest_memfd Alexey Kardashevskiy
2026-02-25 13:55 ` Sean Christopherson
2026-02-26 6:47 ` Alexey Kardashevskiy
2026-02-26 19:27 ` Jason Gunthorpe
2026-02-27 11:03 ` Xu Yilun
2026-02-26 8:19 ` Ackerley Tng
2026-02-26 19:07 ` Jason Gunthorpe
2026-02-26 22:40 ` Sean Christopherson
2026-02-27 0:21 ` Jason Gunthorpe
2026-02-27 0:28 ` Sean Christopherson
2026-02-27 1:09 ` Jason Gunthorpe
2026-02-27 10:35 ` Xu Yilun
2026-02-27 13:18 ` Jason Gunthorpe [this message]
2026-02-28 4:14 ` Xu Yilun
2026-02-28 18:29 ` Jason Gunthorpe
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