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    SubjectRe: [PATCH Part2 v6 25/49] KVM: SVM: Disallow registering memory range from HugeTLB for SNP guest
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    On 6/21/22 01:07, Ashish Kalra wrote:
    > From: Brijesh Singh <brijesh.singh@amd.com>
    >
    > While creating the VM, userspace call the KVM_MEMORY_ENCRYPT_REG_REGION
    > ioctl to register the memory regions for the guest. This registered
    > memory region is typically used as a guest RAM. Later, the guest may
    > issue the page state change (PSC) request that will require splitting
    > the large page into smaller page. If the memory is allocated from the
    > HugeTLB then hypervisor will not be able to split it.
    >
    > Do not allow registering the memory range backed by the HugeTLB until
    > the hypervisor support is added to handle the case.
    >
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > ---
    > arch/x86/kvm/svm/sev.c | 37 +++++++++++++++++++++++++++++++++++++
    > 1 file changed, 37 insertions(+)
    >
    > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
    > index 9e6fc7a94ed7..41b83aa6b5f4 100644
    > --- a/arch/x86/kvm/svm/sev.c
    > +++ b/arch/x86/kvm/svm/sev.c
    > @@ -17,6 +17,7 @@
    > #include <linux/misc_cgroup.h>
    > #include <linux/processor.h>
    > #include <linux/trace_events.h>
    > +#include <linux/hugetlb.h>
    >
    > #include <asm/pkru.h>
    > #include <asm/trapnr.h>
    > @@ -2007,6 +2008,35 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
    > return r;
    > }
    >
    > +static bool is_range_hugetlb(struct kvm *kvm, struct kvm_enc_region *range)
    > +{
    > + struct vm_area_struct *vma;
    > + u64 start, end;
    > + bool ret = true;
    > +
    > + start = range->addr;
    > + end = start + range->size;
    > +
    > + mmap_read_lock(kvm->mm);
    > +
    > + do {
    > + vma = find_vma_intersection(kvm->mm, start, end);
    > + if (!vma)
    > + goto unlock;
    > +
    > + if (is_vm_hugetlb_page(vma))
    > + goto unlock;
    > +
    > + start = vma->vm_end;
    > + } while (end > vma->vm_end);

    Note it's more efficient to only find the first vma and then iterate using
    vma->vm_next. But the details will change when maple tree is merged, and
    likely this patch won't exist after rebasing to UPM anyway...

    > + ret = false;
    > +
    > +unlock:
    > + mmap_read_unlock(kvm->mm);
    > + return ret;
    > +}
    > +
    > int sev_mem_enc_register_region(struct kvm *kvm,
    > struct kvm_enc_region *range)
    > {
    > @@ -2024,6 +2054,13 @@ int sev_mem_enc_register_region(struct kvm *kvm,
    > if (range->addr > ULONG_MAX || range->size > ULONG_MAX)
    > return -EINVAL;
    >
    > + /*
    > + * SEV-SNP does not support the backing pages from the HugeTLB. Verify
    > + * that the registered memory range is not from the HugeTLB.
    > + */
    > + if (sev_snp_guest(kvm) && is_range_hugetlb(kvm, range))
    > + return -EINVAL;
    > +
    > region = kzalloc(sizeof(*region), GFP_KERNEL_ACCOUNT);
    > if (!region)
    > return -ENOMEM;

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