From: Paolo Bonzini <pbonzini@redhat.com>
To: Xu Yilun <yilun.xu@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
seanjc@google.com, michael.roth@amd.com,
isaku.yamahata@intel.com
Subject: Re: [PATCH 06/11] KVM: guest_memfd: Add hook for initializing memory
Date: Tue, 7 May 2024 18:17:49 +0200 [thread overview]
Message-ID: <CABgObfaULPdNbf8yZHEwesDx+KWvt1A+Eps4xY4DkgzhTq9AzA@mail.gmail.com> (raw)
In-Reply-To: <ZiZBjtQvUuuqqKNF@yilunxu-OptiPlex-7050>
On Mon, Apr 22, 2024 at 12:58 PM Xu Yilun <yilun.xu@linux.intel.com> wrote:
> > In some cases, it is necessary to defer the preparation of the pages to
> > handle things like in-place encryption of initial guest memory payloads
> > before marking these pages as 'private'/'guest-owned'. Add an argument
> > (always true for now) to kvm_gmem_get_folio() that allows for the
> > preparation callback to be bypassed. To detect possible issues in
>
> IIUC, we have 2 dedicated flows.
> 1 kvm_gmem_get_pfn() or kvm_gmem_allocate()
> a. kvm_gmem_get_folio()
> b. gmem_prepare() for RMP
>
> 2 in-place encryption or whatever
> a. kvm_gmem_get_folio(FGP_CREAT_ONLY)
> b. in-place encryption
> c. gmem_prepare() for RMP
>
> Could we move gmem_prepare() out of kvm_gmem_get_folio(), then we could
> have straightforward flow for each case, and don't have to have an
> argument to pospone gmem_prepare().
There are 3 flows as you note above - kvm_gmem_get_pfn() and
kvm_gmem_allocate() are different paths but they all need to call the
prepare hook. It is a tempting idea to pull kvm_gmem_prepare_folio()
to the two functions (get_pfn and allocate) but the resulting code is
really ugly due to folio_unlock/folio_put.
> > -static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
> > +#ifdef CONFIG_HAVE_KVM_GMEM_PREPARE
> > +bool __weak kvm_arch_gmem_prepare_needed(struct kvm *kvm)
> > +{
> > + return false;
> > +}
> > +#endif
>
> In which case HAVE_KVM_GMEM_PREPARE is selected but
> gmem_prepare_needed() is never implemented? Then all gmem_prepare stuff
> are actually dead code. Maybe we don't need this weak stub?
It's not needed indeed.
> > + if (prepare) {
> > + int r = kvm_gmem_prepare_folio(inode, index, folio);
> > + if (r < 0) {
> > + folio_unlock(folio);
> > + folio_put(folio);
> > + return ERR_PTR(r);
> > + }
> > + }
> > +
>
> Do we still need to prepare the page if it is hwpoisoned? I see the
> hwpoisoned check is outside, in kvm_gmem_get_pfn().
Yep, it can be moved here.
Paolo
next prev parent reply other threads:[~2024-05-07 16:18 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-04 18:50 [PATCH 00/11] KVM: guest_memfd: New hooks and functionality for SEV-SNP and TDX Paolo Bonzini
2024-04-04 18:50 ` [PATCH 01/11] mm: Introduce AS_INACCESSIBLE for encrypted/confidential memory Paolo Bonzini
2024-04-29 13:14 ` Vlastimil Babka
2024-04-04 18:50 ` [PATCH 02/11] KVM: guest_memfd: Use AS_INACCESSIBLE when creating guest_memfd inode Paolo Bonzini
2024-04-29 13:15 ` Vlastimil Babka
2024-04-04 18:50 ` [PATCH 03/11] KVM: guest_memfd: pass error up from filemap_grab_folio Paolo Bonzini
2024-04-04 18:50 ` [PATCH 04/11] filemap: add FGP_CREAT_ONLY Paolo Bonzini
2024-04-25 5:52 ` Paolo Bonzini
2024-04-29 13:26 ` Vlastimil Babka
2024-04-04 18:50 ` [PATCH 05/11] KVM: guest_memfd: limit overzealous WARN Paolo Bonzini
2024-04-04 18:50 ` [PATCH 06/11] KVM: guest_memfd: Add hook for initializing memory Paolo Bonzini
2024-04-22 10:53 ` Xu Yilun
2024-05-07 16:17 ` Paolo Bonzini [this message]
2024-04-04 18:50 ` [PATCH 07/11] KVM: guest_memfd: extract __kvm_gmem_get_pfn() Paolo Bonzini
2024-04-09 23:35 ` Michael Roth
2024-04-24 22:34 ` Sean Christopherson
2024-04-24 22:59 ` Sean Christopherson
2024-04-04 18:50 ` [PATCH 08/11] KVM: guest_memfd: extract __kvm_gmem_punch_hole() Paolo Bonzini
2024-04-04 18:50 ` [PATCH 09/11] KVM: guest_memfd: Add interface for populating gmem pages with user data Paolo Bonzini
2024-04-22 14:44 ` Xu Yilun
2024-04-23 23:50 ` Isaku Yamahata
2024-04-24 22:24 ` Sean Christopherson
2024-04-25 1:12 ` Isaku Yamahata
2024-04-25 6:01 ` Paolo Bonzini
2024-04-25 16:00 ` Sean Christopherson
2024-04-25 16:51 ` Isaku Yamahata
2024-04-26 5:44 ` Paolo Bonzini
2024-04-26 17:15 ` Isaku Yamahata
2024-04-26 5:41 ` Paolo Bonzini
2024-04-26 15:17 ` Sean Christopherson
2024-04-24 22:32 ` Sean Christopherson
2024-04-25 5:56 ` Paolo Bonzini
2024-04-04 18:50 ` [PATCH 10/11] KVM: guest_memfd: Add hook for invalidating memory Paolo Bonzini
2024-04-04 18:50 ` [PATCH 11/11] KVM: x86: Add gmem hook for determining max NPT mapping level Paolo Bonzini
2024-04-09 23:46 ` Michael Roth
2024-04-19 18:26 ` Isaku Yamahata
2024-04-22 14:52 ` Xu Yilun
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