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    SubjectRe: [RFC 06/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory
    Date
    "Kirill A. Shutemov" <kirill@shutemov.name> writes:

    > New helpers copy_from_guest()/copy_to_guest() to be used if KVM memory
    > protection feature is enabled.
    >
    > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > ---
    > include/linux/kvm_host.h | 4 +++
    > virt/kvm/kvm_main.c | 78 ++++++++++++++++++++++++++++++++++------
    > 2 files changed, 72 insertions(+), 10 deletions(-)
    >
    > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    > index 131cc1527d68..bd0bb600f610 100644
    > --- a/include/linux/kvm_host.h
    > +++ b/include/linux/kvm_host.h
    > @@ -503,6 +503,7 @@ struct kvm {
    > struct srcu_struct srcu;
    > struct srcu_struct irq_srcu;
    > pid_t userspace_pid;
    > + bool mem_protected;
    > };
    >
    > #define kvm_err(fmt, ...) \
    > @@ -727,6 +728,9 @@ void kvm_set_pfn_dirty(kvm_pfn_t pfn);
    > void kvm_set_pfn_accessed(kvm_pfn_t pfn);
    > void kvm_get_pfn(kvm_pfn_t pfn);
    >
    > +int copy_from_guest(void *data, unsigned long hva, int len);
    > +int copy_to_guest(unsigned long hva, const void *data, int len);
    > +
    > void kvm_release_pfn(kvm_pfn_t pfn, bool dirty, struct gfn_to_pfn_cache *cache);
    > int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
    > int len);
    > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    > index 731c1e517716..033471f71dae 100644
    > --- a/virt/kvm/kvm_main.c
    > +++ b/virt/kvm/kvm_main.c
    > @@ -2248,8 +2248,48 @@ static int next_segment(unsigned long len, int offset)
    > return len;
    > }
    >
    > +int copy_from_guest(void *data, unsigned long hva, int len)
    > +{
    > + int offset = offset_in_page(hva);
    > + struct page *page;
    > + int npages, seg;
    > +
    > + while ((seg = next_segment(len, offset)) != 0) {
    > + npages = get_user_pages_unlocked(hva, 1, &page, 0);
    > + if (npages != 1)
    > + return -EFAULT;
    > + memcpy(data, page_address(page) + offset, seg);
    > + put_page(page);
    > + len -= seg;
    > + hva += seg;
    > + offset = 0;
    > + }
    > +
    > + return 0;
    > +}
    > +
    > +int copy_to_guest(unsigned long hva, const void *data, int len)
    > +{
    > + int offset = offset_in_page(hva);
    > + struct page *page;
    > + int npages, seg;
    > +
    > + while ((seg = next_segment(len, offset)) != 0) {
    > + npages = get_user_pages_unlocked(hva, 1, &page, FOLL_WRITE);
    > + if (npages != 1)
    > + return -EFAULT;
    > + memcpy(page_address(page) + offset, data, seg);
    > + put_page(page);
    > + len -= seg;
    > + hva += seg;
    > + offset = 0;
    > + }
    > + return 0;
    > +}
    > +
    > static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
    > - void *data, int offset, int len)
    > + void *data, int offset, int len,
    > + bool protected)
    > {
    > int r;
    > unsigned long addr;
    > @@ -2257,7 +2297,10 @@ static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
    > addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
    > if (kvm_is_error_hva(addr))
    > return -EFAULT;
    > - r = __copy_from_user(data, (void __user *)addr + offset, len);
    > + if (protected)
    > + r = copy_from_guest(data, addr + offset, len);
    > + else
    > + r = __copy_from_user(data, (void __user *)addr + offset, len);
    > if (r)
    > return -EFAULT;
    > return 0;
    > @@ -2268,7 +2311,8 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
    > {
    > struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
    >
    > - return __kvm_read_guest_page(slot, gfn, data, offset, len);
    > + return __kvm_read_guest_page(slot, gfn, data, offset, len,
    > + kvm->mem_protected);
    > }
    > EXPORT_SYMBOL_GPL(kvm_read_guest_page);
    >
    > @@ -2277,7 +2321,8 @@ int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data,
    > {
    > struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
    >
    > - return __kvm_read_guest_page(slot, gfn, data, offset, len);
    > + return __kvm_read_guest_page(slot, gfn, data, offset, len,
    > + vcpu->kvm->mem_protected);

    Personally, I would've just added 'struct kvm' pointer to 'struct
    kvm_memory_slot' to be able to extract 'mem_protected' info when
    needed. This will make the patch much smaller.

    > }
    > EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_page);
    >
    > @@ -2350,7 +2395,8 @@ int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa,
    > EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_atomic);
    >
    > static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
    > - const void *data, int offset, int len)
    > + const void *data, int offset, int len,
    > + bool protected)
    > {
    > int r;
    > unsigned long addr;
    > @@ -2358,7 +2404,11 @@ static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
    > addr = gfn_to_hva_memslot(memslot, gfn);
    > if (kvm_is_error_hva(addr))
    > return -EFAULT;
    > - r = __copy_to_user((void __user *)addr + offset, data, len);
    > +
    > + if (protected)
    > + r = copy_to_guest(addr + offset, data, len);
    > + else
    > + r = __copy_to_user((void __user *)addr + offset, data, len);

    All users of copy_to_guest() will have to have the same 'if (protected)'
    check, right? Why not move the check to copy_to/from_guest() then?

    > if (r)
    > return -EFAULT;
    > mark_page_dirty_in_slot(memslot, gfn);
    > @@ -2370,7 +2420,8 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn,
    > {
    > struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
    >
    > - return __kvm_write_guest_page(slot, gfn, data, offset, len);
    > + return __kvm_write_guest_page(slot, gfn, data, offset, len,
    > + kvm->mem_protected);
    > }
    > EXPORT_SYMBOL_GPL(kvm_write_guest_page);
    >
    > @@ -2379,7 +2430,8 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn,
    > {
    > struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
    >
    > - return __kvm_write_guest_page(slot, gfn, data, offset, len);
    > + return __kvm_write_guest_page(slot, gfn, data, offset, len,
    > + vcpu->kvm->mem_protected);
    > }
    > EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page);
    >
    > @@ -2495,7 +2547,10 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
    > if (unlikely(!ghc->memslot))
    > return kvm_write_guest(kvm, gpa, data, len);
    >
    > - r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
    > + if (kvm->mem_protected)
    > + r = copy_to_guest(ghc->hva + offset, data, len);
    > + else
    > + r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
    > if (r)
    > return -EFAULT;
    > mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT);
    > @@ -2530,7 +2585,10 @@ int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
    > if (unlikely(!ghc->memslot))
    > return kvm_read_guest(kvm, ghc->gpa, data, len);
    >
    > - r = __copy_from_user(data, (void __user *)ghc->hva, len);
    > + if (kvm->mem_protected)
    > + r = copy_from_guest(data, ghc->hva, len);
    > + else
    > + r = __copy_from_user(data, (void __user *)ghc->hva, len);
    > if (r)
    > return -EFAULT;

    --
    Vitaly

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