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    SubjectRe: [PATCH v3 04/10] KVM: Implement kvm_put_guest()
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    On 22/08/2019 11:29, Jonathan Cameron wrote:
    > On Wed, 21 Aug 2019 16:36:50 +0100
    > Steven Price <steven.price@arm.com> 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.
    >>
    >> 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; \
    >
    > Why initialize __ret?

    Good question. Actually looking at this again if I reorder this to be
    pessimistic I can make it shorter:

    int __ret = -EFAULT;

    if (!kvm_is_error_hva(__addr))
    __ret = put_user(value, __uaddr);
    if (!__ret)
    mark_page_dirty(kvm, gfn);
    __ret;

    Thanks for taking a look.

    Steve

    >> + \
    >> + 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);
    >
    >
    >
    > _______________________________________________
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    > linux-arm-kernel@lists.infradead.org
    > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
    >

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