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SubjectRe: [PATCH v3 04/10] KVM: Implement kvm_put_guest()
On Wed, Aug 21, 2019 at 04:36:50PM +0100, Steven Price wrote:
> kvm_put_guest() is analogous to put_user() - it writes a single value to
> the guest physical address. The implementation is built upon put_user()
> and so it has the same single copy atomic properties.

What you mean by "single copy atomic"? I.e. what guarantees does
put_user() provide that __copy_to_user() does not?

>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> include/linux/kvm_host.h | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index fcb46b3374c6..e154a1897e20 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -746,6 +746,30 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> unsigned long len);
> int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> gpa_t gpa, unsigned long len);
> +
> +#define __kvm_put_guest(kvm, gfn, offset, value, type) \
> +({ \
> + unsigned long __addr = gfn_to_hva(kvm, gfn); \
> + type __user *__uaddr = (type __user *)(__addr + offset); \
> + int __ret = 0; \
> + \
> + if (kvm_is_error_hva(__addr)) \
> + __ret = -EFAULT; \
> + else \
> + __ret = put_user(value, __uaddr); \
> + if (!__ret) \
> + mark_page_dirty(kvm, gfn); \
> + __ret; \
> +})
> +
> +#define kvm_put_guest(kvm, gpa, value, type) \
> +({ \
> + gpa_t __gpa = gpa; \
> + struct kvm *__kvm = kvm; \
> + __kvm_put_guest(__kvm, __gpa >> PAGE_SHIFT, \
> + offset_in_page(__gpa), (value), type); \
> +})
> +
> int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len);
> int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len);
> struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn);
> --
> 2.20.1
>

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