linux-kernel - Re: [RFC PATCH v1 05/37] KVM: guest_memfd: Wire up kvm_get_memory

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Message-ID: <aYRBEJSan8eoT8xw@yilunxu-OptiPlex-7050>
Date: Thu, 5 Feb 2026 15:04:48 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Sean Christopherson <seanjc@...gle.com>,
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Subject: Re: [RFC PATCH v1 05/37] KVM: guest_memfd: Wire up
 kvm_get_memory_attributes() to per-gmem attributes

On Wed, Feb 04, 2026 at 08:47:15AM -0400, Jason Gunthorpe wrote:
> On Wed, Feb 04, 2026 at 12:43:16PM +0800, Xu Yilun wrote:
> > > Which means we need VFIO to know what they are, and hopefully it is
> > > just static based on the TDISP reports..
> > 
> > I don't think VMM need to check TDISP report. The only special thing is
> > the MSI-X mixed pages which can be figured out by standard PCI
> > discovery.
> 
> Either that or follow along with the guests's choices on
> shared/private.
> 
> We can't let VFIO mmap a private MMIO page, so it has to know which
> pages are private at any moment, and it can't guess.

No we could only let VFIO mmap MMIO pages that need emulation (like this
MSI-X mixed page). MMIOs in such page cannot be assigned to guest so no
way to convert to private.

We don't allow VFIO mmap all asigned MMIO pages, no matter they will be
private or shared. They are assigned to guest, so host don't touch them.
Does that make sense?

> 
> Jason