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Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create
From: |
Huang, Kai |
Subject: |
Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory |
Date: |
Fri, 23 Dec 2022 00:50:22 +0000 |
User-agent: |
Evolution 3.44.4 (3.44.4-2.fc36) |
On Thu, 2022-12-22 at 18:15 +0000, Sean Christopherson wrote:
> On Wed, Dec 21, 2022, Chao Peng wrote:
> > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote:
> > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote:
> > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote:
> > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote:
> > > But for non-restricted-mem case, it is correct for KVM to decrease page's
> > > refcount after setting up mapping in the secondary mmu, otherwise the
> > > page will
> > > be pinned by KVM for normal VM (since KVM uses GUP to get the page).
> >
> > That's true. Actually even true for restrictedmem case, most likely we
> > will still need the kvm_release_pfn_clean() for KVM generic code. On one
> > side, other restrictedmem users like pKVM may not require page pinning
> > at all. On the other side, see below.
> >
> > >
> > > So what we are expecting is: for KVM if the page comes from restricted
> > > mem, then
> > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM
> > > should.
>
> No, requiring the user (KVM) to guard against lack of support for page
> migration
> in restricted mem is a terrible API. It's totally fine for restricted mem to
> not
> support page migration until there's a use case, but punting the problem to
> KVM
> is not acceptable. Restricted mem itself doesn't yet support page migration,
> e.g. explosions would occur even if KVM wanted to allow migration since there
> is
> no notification to invalidate existing mappings.
>
>
Yes totally agree (I also replied separately).
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, (continued)
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Huang, Kai, 2022/12/13
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Chao Peng, 2022/12/19
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Huang, Kai, 2022/12/19
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Chao Peng, 2022/12/20
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Huang, Kai, 2022/12/20
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Chao Peng, 2022/12/21
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Huang, Kai, 2022/12/21
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Chao Peng, 2022/12/23
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Sean Christopherson, 2022/12/22
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory,
Huang, Kai <=
- Re: [PATCH v10 1/9] mm: Introduce memfd_restricted system call to create restricted user memory, Chao Peng, 2022/12/23
[PATCH v10 2/9] KVM: Introduce per-page memory attributes, Chao Peng, 2022/12/02