Re: [Xen-devel] [PATCH v3 23/25] x86/HVM: make use of new read-modify-write emulator hook

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 07 December 2017 14:18
> To: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Paul Durrant
> <Paul.Durrant@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>
> Subject: [PATCH v3 23/25] x86/HVM: make use of new read-modify-write
> emulator hook
> 
> ..., at least as far as currently possible, i.e. when a mapping can be
> obtained.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
> v3: New.
> 
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -1187,6 +1187,61 @@ static int hvmemul_write(
>      return X86EMUL_OKAY;
>  }
> 
> +static int hvmemul_rmw(
> +    enum x86_segment seg,
> +    unsigned long offset,
> +    unsigned int bytes,
> +    uint32_t *eflags,
> +    struct x86_emulate_state *state,
> +    struct x86_emulate_ctxt *ctxt)
> +{
> +    struct hvm_emulate_ctxt *hvmemul_ctxt =
> +        container_of(ctxt, struct hvm_emulate_ctxt, ctxt);
> +    unsigned long addr, reps = 1;
> +    uint32_t pfec = PFEC_page_present | PFEC_write_access;
> +    struct hvm_vcpu_io *vio = &current->arch.hvm_vcpu.hvm_io;
> +    int rc;
> +    void *mapping;
> +
> +    rc = hvmemul_virtual_to_linear(
> +        seg, offset, bytes, &reps, hvm_access_write, hvmemul_ctxt, &addr);
> +    if ( rc != X86EMUL_OKAY || !bytes )
> +        return rc;
> +
> +    if ( is_x86_system_segment(seg) )
> +        pfec |= PFEC_implicit;
> +    else if ( hvmemul_ctxt->seg_reg[x86_seg_ss].dpl == 3 )
> +        pfec |= PFEC_user_mode;
> +
> +    mapping = hvmemul_map_linear_addr(addr, bytes, pfec,
> hvmemul_ctxt);
> +    if ( IS_ERR(mapping) )
> +        return ~PTR_ERR(mapping);
> +
> +    if ( mapping )
> +    {
> +        rc = x86_emul_rmw(mapping, bytes, eflags, state, ctxt);
> +        hvmemul_unmap_linear_addr(mapping, addr, bytes, hvmemul_ctxt);
> +    }
> +    else
> +    {
> +        unsigned long data = 0;
> +        bool_t known_gpfn = vio->mmio_access.write_access &&
> +                            vio->mmio_gla == (addr & PAGE_MASK);
> +
> +        if ( bytes > sizeof(data) )
> +            return X86EMUL_UNHANDLEABLE;
> +        rc = hvmemul_linear_mmio_read(addr, bytes, &data, pfec,
> hvmemul_ctxt,
> +                                      known_gpfn);
> +        if ( rc == X86EMUL_OKAY )
> +            rc = x86_emul_rmw(&data, bytes, eflags, state, ctxt);
> +        if ( rc == X86EMUL_OKAY )
> +            rc = hvmemul_linear_mmio_write(addr, bytes, &data, pfec,
> +                                           hvmemul_ctxt, known_gpfn);
> +    }
> +
> +    return rc;
> +}
> +
>  static int hvmemul_write_discard(
>      enum x86_segment seg,
>      unsigned long offset,
> @@ -2157,6 +2212,7 @@ static const struct x86_emulate_ops hvm_
>      .read          = hvmemul_read,
>      .insn_fetch    = hvmemul_insn_fetch,
>      .write         = hvmemul_write,
> +    .rmw           = hvmemul_rmw,
>      .cmpxchg       = hvmemul_cmpxchg,
>      .validate      = hvmemul_validate,
>      .rep_ins       = hvmemul_rep_ins,
> 
> 


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