On Tue, Mar 29, 2022 at 07:13:00PM +0000, Sean Christopherson wrote:
> On Thu, Mar 10, 2022, Chao Peng wrote:
> > KVM_MEM_PRIVATE is not exposed by default but architecture code can turn
> > on it by implementing kvm_arch_private_memory_supported().
> >
> > Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > ---
> > include/linux/kvm_host.h | 1 +
> > virt/kvm/kvm_main.c | 24 +++++++++++++++++++-----
> > 2 files changed, 20 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 186b9b981a65..0150e952a131 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -1432,6 +1432,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
> > int kvm_arch_post_init_vm(struct kvm *kvm);
> > void kvm_arch_pre_destroy_vm(struct kvm *kvm);
> > int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> > +bool kvm_arch_private_memory_supported(struct kvm *kvm);
> >
> > #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> > /*
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 52319f49d58a..df5311755a40 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1485,10 +1485,19 @@ static void kvm_replace_memslot(struct kvm *kvm,
> > }
> > }
> >
> > -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
> > +bool __weak kvm_arch_private_memory_supported(struct kvm *kvm)
> > +{
> > + return false;
> > +}
> > +
> > +static int check_memory_region_flags(struct kvm *kvm,
> > + const struct kvm_userspace_memory_region *mem)
> > {
> > u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> >
> > + if (kvm_arch_private_memory_supported(kvm))
> > + valid_flags |= KVM_MEM_PRIVATE;
> > +
> > #ifdef __KVM_HAVE_READONLY_MEM
> > valid_flags |= KVM_MEM_READONLY;
> > #endif
> > @@ -1900,7 +1909,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > int as_id, id;
> > int r;
> >
> > - r = check_memory_region_flags(mem);
> > + r = check_memory_region_flags(kvm, mem);
> > if (r)
> > return r;
> >
> > @@ -1913,10 +1922,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > return -EINVAL;
> > if (mem->guest_phys_addr & (PAGE_SIZE - 1))
> > return -EINVAL;
> > - /* We can read the guest memory with __xxx_user() later on. */
> > if ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
> > - (mem->userspace_addr != untagged_addr(mem->userspace_addr)) ||
> > - !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> > + (mem->userspace_addr != untagged_addr(mem->userspace_addr)))
> > + return -EINVAL;
> > + /* We can read the guest memory with __xxx_user() later on. */
> > + if (!(mem->flags & KVM_MEM_PRIVATE) &&
> > + !access_ok((void __user *)(unsigned long)mem->userspace_addr,
>
> This should sanity check private_offset for private memslots. At a bare minimum,
> wrapping should be disallowed.
Will add this.
>
> > mem->memory_size))
> > return -EINVAL;
> > if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> > @@ -1957,6 +1968,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages)
> > return -EINVAL;
> > } else { /* Modify an existing slot. */
> > + /* Private memslots are immutable, they can only be deleted. */
> > + if (mem->flags & KVM_MEM_PRIVATE)
> > + return -EINVAL;
>
> These sanity checks belong in "KVM: Register private memslot to memory backing store",
> e.g. that patch is "broken" without the immutability restriction. It's somewhat moot
> because the code is unreachable, but it makes reviewing confusing/difficult.
>
> But rather than move the sanity checks back, I think I'd prefer to pull all of patch 10
> here. I think it also makes sense to drop "KVM: Use memfile_pfn_ops to obtain pfn for
> private pages" and add the pointer in "struct kvm_memory_slot" in patch "KVM: Extend the
> memslot to support fd-based private memory", with the use of the ops folded into
> "KVM: Handle page fault for private memory". Adding code to KVM and KVM-x86 in a single
> patch is ok, and overall makes things easier to review because the new helpers have a
> user right away, especially since there will be #ifdeffery.
>
> I.e. end up with something like:
>
> mm: Introduce memfile_notifier
> mm/shmem: Restrict MFD_INACCESSIBLE memory against RLIMIT_MEMLOCK
> KVM: Extend the memslot to support fd-based private memory
> KVM: Use kvm_userspace_memory_region_ext
> KVM: Add KVM_EXIT_MEMORY_ERROR exit
> KVM: Handle page fault for private memory
> KVM: Register private memslot to memory backing store
> KVM: Zap existing KVM mappings when pages changed in the private fd
> KVM: Enable and expose KVM_MEM_PRIVATE
Thanks for the suggestion. That makes sense.
Chao
>
> > if ((mem->userspace_addr != old->userspace_addr) ||
> > (npages != old->npages) ||
> > ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
> > --
> > 2.17.1
> >
