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    Subject[PATCH 4.14 031/173] KVM: arm64: Only sign-extend MMIO up to register width
    Date
    From: Christoffer Dall <christoffer.dall@arm.com>

    commit b6ae256afd32f96bec0117175b329d0dd617655e upstream.

    On AArch64 you can do a sign-extended load to either a 32-bit or 64-bit
    register, and we should only sign extend the register up to the width of
    the register as specified in the operation (by using the 32-bit Wn or
    64-bit Xn register specifier).

    As it turns out, the architecture provides this decoding information in
    the SF ("Sixty-Four" -- how cute...) bit.

    Let's take advantage of this with the usual 32-bit/64-bit header file
    dance and do the right thing on AArch64 hosts.

    Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
    Signed-off-by: Marc Zyngier <maz@kernel.org>
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20191212195055.5541-1-christoffer.dall@arm.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/include/asm/kvm_emulate.h | 5 +++++
    arch/arm/include/asm/kvm_mmio.h | 2 ++
    arch/arm64/include/asm/kvm_emulate.h | 5 +++++
    arch/arm64/include/asm/kvm_mmio.h | 6 ++----
    virt/kvm/arm/mmio.c | 6 ++++++
    5 files changed, 20 insertions(+), 4 deletions(-)

    --- a/arch/arm/include/asm/kvm_emulate.h
    +++ b/arch/arm/include/asm/kvm_emulate.h
    @@ -144,6 +144,11 @@ static inline bool kvm_vcpu_dabt_issext(
    return kvm_vcpu_get_hsr(vcpu) & HSR_SSE;
    }

    +static inline bool kvm_vcpu_dabt_issf(const struct kvm_vcpu *vcpu)
    +{
    + return false;
    +}
    +
    static inline int kvm_vcpu_dabt_get_rd(struct kvm_vcpu *vcpu)
    {
    return (kvm_vcpu_get_hsr(vcpu) & HSR_SRT_MASK) >> HSR_SRT_SHIFT;
    --- a/arch/arm/include/asm/kvm_mmio.h
    +++ b/arch/arm/include/asm/kvm_mmio.h
    @@ -26,6 +26,8 @@
    struct kvm_decode {
    unsigned long rt;
    bool sign_extend;
    + /* Not used on 32-bit arm */
    + bool sixty_four;
    };

    void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
    --- a/arch/arm64/include/asm/kvm_emulate.h
    +++ b/arch/arm64/include/asm/kvm_emulate.h
    @@ -188,6 +188,11 @@ static inline bool kvm_vcpu_dabt_issext(
    return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SSE);
    }

    +static inline bool kvm_vcpu_dabt_issf(const struct kvm_vcpu *vcpu)
    +{
    + return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SF);
    +}
    +
    static inline int kvm_vcpu_dabt_get_rd(const struct kvm_vcpu *vcpu)
    {
    return (kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SRT_MASK) >> ESR_ELx_SRT_SHIFT;
    --- a/arch/arm64/include/asm/kvm_mmio.h
    +++ b/arch/arm64/include/asm/kvm_mmio.h
    @@ -21,13 +21,11 @@
    #include <linux/kvm_host.h>
    #include <asm/kvm_arm.h>

    -/*
    - * This is annoying. The mmio code requires this, even if we don't
    - * need any decoding. To be fixed.
    - */
    struct kvm_decode {
    unsigned long rt;
    bool sign_extend;
    + /* Witdth of the register accessed by the faulting instruction is 64-bits */
    + bool sixty_four;
    };

    void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
    --- a/virt/kvm/arm/mmio.c
    +++ b/virt/kvm/arm/mmio.c
    @@ -117,6 +117,9 @@ int kvm_handle_mmio_return(struct kvm_vc
    data = (data ^ mask) - mask;
    }

    + if (!vcpu->arch.mmio_decode.sixty_four)
    + data = data & 0xffffffff;
    +
    trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
    &data);
    data = vcpu_data_host_to_guest(vcpu, data, len);
    @@ -137,6 +140,7 @@ static int decode_hsr(struct kvm_vcpu *v
    unsigned long rt;
    int access_size;
    bool sign_extend;
    + bool sixty_four;

    if (kvm_vcpu_dabt_iss1tw(vcpu)) {
    /* page table accesses IO mem: tell guest to fix its TTBR */
    @@ -150,11 +154,13 @@ static int decode_hsr(struct kvm_vcpu *v

    *is_write = kvm_vcpu_dabt_iswrite(vcpu);
    sign_extend = kvm_vcpu_dabt_issext(vcpu);
    + sixty_four = kvm_vcpu_dabt_issf(vcpu);
    rt = kvm_vcpu_dabt_get_rd(vcpu);

    *len = access_size;
    vcpu->arch.mmio_decode.sign_extend = sign_extend;
    vcpu->arch.mmio_decode.rt = rt;
    + vcpu->arch.mmio_decode.sixty_four = sixty_four;

    return 0;
    }

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