On Wed, Mar 06, 2019 at 05:00:15PM +1100, Suraj Jitindar Singh wrote:
> Implement the function kvm_copy_guest() to be used to perform a memory
> copy from one guest physical address to another of a variable length.
>
> This performs similar functionality as the kvm_read_guest() and
> kvm_write_guest() functions, except both addresses point to guest memory.
> This performs a copy in place using raw_copy_in_user() to avoid having to
> buffer the data.
>
> The guest memory can reside in different memslots and the copy length
> can span memslots.
>
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
>
> ---
>
> I suspect additional checking may be required around the raw_copy_in_user()
> call.
>
> ---
> include/linux/kvm_host.h | 1 +
> virt/kvm/kvm_main.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 70 insertions(+)
>
...
> +static int next_segment_many(unsigned long len, int offset1, int offset2)
> +{
> + int size = min(PAGE_SIZE - offset1, PAGE_SIZE - offset2);
> +
> + if (len > size)
> + return size;
> + else
> + return len;
> +}
> +
> +int kvm_copy_guest(struct kvm *kvm, gpa_t to, gpa_t from, unsigned long len)
> +{
> + struct kvm_memory_slot *to_memslot = NULL;
> + struct kvm_memory_slot *from_memslot = NULL;
> + gfn_t to_gfn = to >> PAGE_SHIFT;
> + gfn_t from_gfn = from >> PAGE_SHIFT;
> + int seg;
> + int to_offset = offset_in_page(to);
> + int from_offset = offset_in_page(from);
> + int ret;
> +
> + while ((seg = next_segment_many(len, to_offset, from_offset)) != 0) {
> + if (!to_memslot || (to_gfn >= (to_memslot->base_gfn +
> + to_memslot->npages)))
> + to_memslot = gfn_to_memslot(kvm, to_gfn);
> + if (!from_memslot || (from_gfn >= (from_memslot->base_gfn +
> + from_memslot->npages)))
> + from_memslot = gfn_to_memslot(kvm, from_gfn);
> +
> + ret = __kvm_copy_guest_page(to_memslot, to_gfn, to_offset,
> + from_memslot, from_gfn, from_offset,
> + seg);
> + if (ret < 0)
> + return ret;
> +
> + to_offset = (to_offset + seg) & (PAGE_SIZE - 1);
> + from_offset = (from_offset + seg) & (PAGE_SIZE - 1);
> + len -= seg;
> + if (!to_offset)
> + to_gfn += 1;
> + if (!from_offset)
> + from_gfn += 1;
> + }
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_copy_guest);
Is there a need to support spanning multiple pages at this time? Your use
case always accesses exactly a page and requires both dst and src to be
page aligned. I.e. provide just kvm_copy_guest_page() for simplicity.
> +
> static int __kvm_gfn_to_hva_cache_init(struct kvm_memslots *slots,
> struct gfn_to_hva_cache *ghc,
> gpa_t gpa, unsigned long len)
> --
> 2.13.6
>
