Re: [PATCH v10 046/108] KVM: Add flags to struct kvm_gfn_range

Huang, Kai
2022-12-15T22:41:36Z

On Thu, 2022-12-15 at 14:10 -0800, Isaku Yamahata wrote:
> On Wed, Dec 14, 2022 at 10:51:31AM +0000,
> "Huang, Kai" <kai.huang@intel.com> wrote:
>
> > On Sat, 2022-10-29 at 23:22 -0700, isaku.yamahata@intel.com wrote:
> > > From: Isaku Yamahata <isaku.yamahata@intel.com>
> > >
> > > kvm_unmap_gfn_range() needs to know the reason of the callback for TDX.
> > > mmu notifier, set memattr ioctl or restrictedmem notifier. Based on the
> > > reason, TDX changes the behavior. For mmu notifier, it's the operation on
> > > shared memory slot to zap shared PTE. For set memattr, private<->shared
> > > conversion, zap the original PTE. For restrictedmem, it's a hint that TDX
> > > can ignore.
> >
> > Could you elaborate why restricted memfd notifier can be ignored? IIUC if
> > userspace punch a hole, the pages within the hole will be de-allocated. So why
> > can such notifier be ignored?
>
> Because set-memory-attribute ioctl is expected to follow the callback from
> restrictedmem. So set memory attributes can do de-allocation. I wanted to avoid
> zapping twice.

Even this is true, the punch hole can be done alone w/o being followed by
set_memory_attribute(), correct? Your explanation doesn't seem to be
reasonable?

At least, you need to explain the semantics of how to use "punch hole" and
set_memory_attributes() clearly in the changelog. Otherwise it's hard for
people to review.