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Wed, 24 Apr 2024 15:59:59 -0700 (PDT) Date: Wed, 24 Apr 2024 15:59:57 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240404185034.3184582-1-pbonzini@redhat.com> <20240404185034.3184582-8-pbonzini@redhat.com> Message-ID: Subject: Re: [PATCH 07/11] KVM: guest_memfd: extract __kvm_gmem_get_pfn() From: Sean Christopherson To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, michael.roth@amd.com, isaku.yamahata@intel.com Content-Type: text/plain; charset="us-ascii" On Wed, Apr 24, 2024, Sean Christopherson wrote: > On Thu, Apr 04, 2024, Paolo Bonzini wrote: > > In preparation for adding a function that walks a set of pages > > provided by userspace and populates them in a guest_memfd, > > add a version of kvm_gmem_get_pfn() that has a "bool prepare" > > argument and passes it down to kvm_gmem_get_folio(). > > > > Populating guest memory has to call repeatedly __kvm_gmem_get_pfn() > > on the same file, so make the new function take struct file*. > > > > Signed-off-by: Paolo Bonzini > > --- > > virt/kvm/guest_memfd.c | 38 +++++++++++++++++++++++--------------- > > 1 file changed, 23 insertions(+), 15 deletions(-) > > > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > > index 486748e65f36..a537a7e63ab5 100644 > > --- a/virt/kvm/guest_memfd.c > > +++ b/virt/kvm/guest_memfd.c > > @@ -540,33 +540,29 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot) > > fput(file); > > } > > > > -int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, > > - gfn_t gfn, kvm_pfn_t *pfn, int *max_order) > > +static int __kvm_gmem_get_pfn(struct file *file, struct kvm_memory_slot *slot, > > + gfn_t gfn, kvm_pfn_t *pfn, int *max_order, bool prepare) > > I genuinely don't know what it means to "prepare" a guest_memfd. I see it becomes > > if (!prepare) > fgp_flags |= FGP_CREAT_ONLY; > > but I find the name "prepare" to be extremely unhelpful. Ah, I'm blind. Maybe "do_prepare", or "do_arch_prepare"? To make it clear that it's a command, not a description of the operation (which is how I first read it). And I feel like overloading it to also mean FGP_CREAT_ONLY when _not_ preparing the memory is odd. if (prepare) { int r = kvm_gmem_prepare_folio(inode, index, folio); if (r < 0) { folio_unlock(folio); folio_put(folio); return ERR_PTR(r); } } Instead of "prepare" as a command, would it make sense to describe the "populating" case? Because I think it's more intuitive that populating _needs_ to operate on new, unprepared data.