Re: [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared

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To: Fuad Tabba <tabba@xxxxxxxxxx>
Subject: Re: [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
From: Jason Gunthorpe <jgg@xxxxxxxxxx>
Date: Thu, 10 Oct 2024 11:37:16 -0300
Cc: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, linux-arm-msm@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, pbonzini@xxxxxxxxxx, chenhuacai@xxxxxxxxxx, mpe@xxxxxxxxxxxxxx, anup@xxxxxxxxxxxxxx, paul.walmsley@xxxxxxxxxx, palmer@xxxxxxxxxxx, aou@xxxxxxxxxxxxxxxxx, seanjc@xxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, brauner@xxxxxxxxxx, willy@xxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, xiaoyao.li@xxxxxxxxx, yilun.xu@xxxxxxxxx, chao.p.peng@xxxxxxxxxxxxxxx, jarkko@xxxxxxxxxx, amoorthy@xxxxxxxxxx, dmatlack@xxxxxxxxxx, yu.c.zhang@xxxxxxxxxxxxxxx, isaku.yamahata@xxxxxxxxx, mic@xxxxxxxxxxx, vbabka@xxxxxxx, vannapurve@xxxxxxxxxx, ackerleytng@xxxxxxxxxx, mail@xxxxxxxxxxxxxxxxxxxxx, david@xxxxxxxxxx, michael.roth@xxxxxxx, wei.w.wang@xxxxxxxxx, liam.merwick@xxxxxxxxxx, isaku.yamahata@xxxxxxxxx, kirill.shutemov@xxxxxxxxxxxxxxx, suzuki.poulose@xxxxxxx, steven.price@xxxxxxx, quic_eberman@xxxxxxxxxxx, quic_mnalajal@xxxxxxxxxxx, quic_tsoni@xxxxxxxxxxx, quic_svaddagi@xxxxxxxxxxx, quic_cvanscha@xxxxxxxxxxx, quic_pderrin@xxxxxxxxxxx, quic_pheragu@xxxxxxxxxxx, catalin.marinas@xxxxxxx, james.morse@xxxxxxx, yuzenghui@xxxxxxxxxx, oliver.upton@xxxxxxxxx, maz@xxxxxxxxxx, will@xxxxxxxxxx, qperret@xxxxxxxxxx, keirf@xxxxxxxxxx, roypat@xxxxxxxxxxxx, shuah@xxxxxxxxxx, hch@xxxxxxxxxxxxx, rientjes@xxxxxxxxxx, jhubbard@xxxxxxxxxx, fvdl@xxxxxxxxxx, hughd@xxxxxxxxxx, jthoughton@xxxxxxxxxx
In-reply-to: <CA+EHjTwEmXcQhCzGJG1icBzHvWEBUVVH33-ng60ngup6LMcC4Q@mail.gmail.com>
References: <20241010085930.1546800-1-tabba@google.com> <20241010085930.1546800-5-tabba@google.com> <i44qkun5ddu3vwli7dxh27je72ywlrb7m5ercjhvprhleapv6x@52dwi3kwp2zx> <CA+EHjTwOsbNRN=6ZQ4rAJLhpVNifrtmLLs84q4_kOixghaSHBg@mail.gmail.com> <mr26r6uvvvdevwqz6flhnzbqjwkf7ucictnjhk3xsuktwsujh5@ncf57r3v6w6p> <CA+EHjTwEmXcQhCzGJG1icBzHvWEBUVVH33-ng60ngup6LMcC4Q@mail.gmail.com>

On Thu, Oct 10, 2024 at 03:28:38PM +0100, Fuad Tabba wrote:

> I remember discussing this before. One question that I have is, is it
> possible to get a transient pin while the folio lock is held, 

No, you can't lock a folio until you refcount it. That is a basic
requirement for any transient pin.

Jason

References:
- [PATCH v3 00/11] KVM: Restricted mapping of guest_memfd at the host and arm64 support
  - From: Fuad Tabba
- [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
  - From: Fuad Tabba
- Re: [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
  - From: Kirill A. Shutemov
- Re: [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
  - From: Fuad Tabba
- Re: [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
  - From: Kirill A. Shutemov
- Re: [PATCH v3 04/11] KVM: guest_memfd: Allow host to mmap guest_memfd() pages when shared
  - From: Fuad Tabba

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