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    SubjectRe: [PATCH] KVM: Switch 'requests' to be 64-bit (explicitly)
    Date
    On Thu, 2018-07-05 at 14:51 +0100, Mark Rutland wrote:
    > On Sun, Apr 15, 2018 at 12:26:44AM +0200, KarimAllah Ahmed wrote:
    > >
    > > Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
    > > use the size of "requests" instead of the hard-coded '32'.
    > >
    > > That gives us a bit more room again for arch-specific requests as we
    > > already ran out of space for x86 due to the hard-coded check.
    > >
    > > Cc: Paolo Bonzini <pbonzini@redhat.com>
    > > Cc: Radim Krčmář <rkrcmar@redhat.com>
    > > Cc: kvm@vger.kernel.org
    > > Cc: linux-kernel@vger.kernel.org
    > > Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
    > > ---
    > > include/linux/kvm_host.h | 10 +++++-----
    > > 1 file changed, 5 insertions(+), 5 deletions(-)
    > >
    > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    > > index 6930c63..fe4f46b 100644
    > > --- a/include/linux/kvm_host.h
    > > +++ b/include/linux/kvm_host.h
    > > @@ -129,7 +129,7 @@ static inline bool is_error_page(struct page *page)
    > > #define KVM_REQUEST_ARCH_BASE 8
    > >
    > > #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
    > > - BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
    > > + BUILD_BUG_ON((unsigned)(nr) >= (sizeof(((struct kvm_vcpu *)0)->requests) * 8) - KVM_REQUEST_ARCH_BASE); \
    > > (unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
    > > })
    > > #define KVM_ARCH_REQ(nr) KVM_ARCH_REQ_FLAGS(nr, 0)
    > > @@ -223,7 +223,7 @@ struct kvm_vcpu {
    > > int vcpu_id;
    > > int srcu_idx;
    > > int mode;
    > > - unsigned long requests;
    > > + u64 requests;
    >
    > The usual thing to do for bitmaps is something like:
    >
    > #define KVM_REQUEST_NR (KVM_REQUEST_ARCH_BASE + KVM_REQUEST_ARCH_NR)
    >
    > unsigned long requests[BITS_TO_LONGS(NR_KVM_REQUESTS)];
    >
    > >
    > > unsigned long guest_debug;
    > >
    > > int pre_pcpu;
    > > @@ -1122,7 +1122,7 @@ static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
    > > * caller. Paired with the smp_mb__after_atomic in kvm_check_request.
    > > */
    > > smp_wmb();
    > > - set_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
    > > + set_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
    >
    > ... which wouldn't require a void cast to make the bit API functions
    > happy (as these expect a pointer to the first unsigned long in the
    > bitmap).

    Ah, right! Good point.

    Paolo,

    Would you prefer to switch "requests" to a bitmap and 
    update kvm_request_pending to handle this?

    >
    > Thanks,
    > Mark.
    >
    Amazon Development Center Germany GmbH
    Berlin - Dresden - Aachen
    main office: Krausenstr. 38, 10117 Berlin
    Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
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