Re: [PATCH v3] nested SVM: adjust guest handling of structure mappings

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 11/11/13 12:53, Jan Beulich wrote:
> For one, nestedsvm_vmcb_map() error checking must not consist of using
> assertions: Global (permanent) mappings can fail, and hence failure
> needs to be dealt with properly. And non-global (transient) mappings
> can't fail anyway.
>
> And then the I/O port access bitmap handling was broken: It checked
> only to first of the accessed ports rather than each of them.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v3: Add error check to mapping operation in
>     nsvm_vmcb_guest_intercepts_ioio() (pointed out by Andrew Cooper).
>
> --- a/xen/arch/x86/hvm/svm/nestedsvm.c
> +++ b/xen/arch/x86/hvm/svm/nestedsvm.c
> @@ -342,7 +342,7 @@ static int nsvm_vmrun_permissionmap(stru
>      unsigned int i;
>      enum hvm_copy_result ret;
>      unsigned long *ns_viomap;
> -    bool_t ioport_80, ioport_ed;
> +    bool_t ioport_80 = 1, ioport_ed = 1;
>  
>      ns_msrpm_ptr = (unsigned long *)svm->ns_cached_msrpm;
>  
> @@ -360,10 +360,12 @@ static int nsvm_vmrun_permissionmap(stru
>      svm->ns_iomap_pa = ns_vmcb->_iopm_base_pa;
>  
>      ns_viomap = hvm_map_guest_frame_ro(svm->ns_iomap_pa >> PAGE_SHIFT, 0);
> -    ASSERT(ns_viomap != NULL);
> -    ioport_80 = test_bit(0x80, ns_viomap);
> -    ioport_ed = test_bit(0xed, ns_viomap);
> -    hvm_unmap_guest_frame(ns_viomap, 0);
> +    if ( ns_viomap )
> +    {
> +        ioport_80 = test_bit(0x80, ns_viomap);
> +        ioport_ed = test_bit(0xed, ns_viomap);
> +        hvm_unmap_guest_frame(ns_viomap, 0);
> +    }
>  
>      svm->ns_iomap = nestedhvm_vcpu_iomap_get(ioport_80, ioport_ed);
>  
> @@ -866,40 +868,45 @@ nsvm_vmcb_guest_intercepts_msr(unsigned 
>  static int
>  nsvm_vmcb_guest_intercepts_ioio(paddr_t iopm_pa, uint64_t exitinfo1)
>  {
> -    unsigned long iopm_gfn = iopm_pa >> PAGE_SHIFT;
> -    unsigned long *io_bitmap = NULL;
> +    unsigned long gfn = iopm_pa >> PAGE_SHIFT;
> +    unsigned long *io_bitmap;
>      ioio_info_t ioinfo;
>      uint16_t port;
> +    unsigned int size;
>      bool_t enabled;
> -    unsigned long gfn = 0; /* gcc ... */
>  
>      ioinfo.bytes = exitinfo1;
>      port = ioinfo.fields.port;
> +    size = ioinfo.fields.sz32 ? 4 : ioinfo.fields.sz16 ? 2 : 1;
>  
> -    switch (port) {
> -    case 0 ... 32767: /* first 4KB page */
> -        gfn = iopm_gfn;
> +    switch ( port )
> +    {
> +    case 0 ... 8 * PAGE_SIZE - 1: /* first 4KB page */
>          break;
> -    case 32768 ... 65535: /* second 4KB page */
> -        port -= 32768;
> -        gfn = iopm_gfn + 1;
> +    case 8 * PAGE_SIZE ... 2 * 8 * PAGE_SIZE - 1: /* second 4KB page */
> +        port -= 8 * PAGE_SIZE;
> +        ++gfn;
>          break;
>      default:
>          BUG();
>          break;
>      }
>  
> -    io_bitmap = hvm_map_guest_frame_ro(gfn, 0);
> -    if (io_bitmap == NULL) {
> -        gdprintk(XENLOG_ERR,
> -            "IOIO intercept: mapping of permission map failed\n");
> -        return NESTEDHVM_VMEXIT_ERROR;
> +    for ( io_bitmap = hvm_map_guest_frame_ro(gfn, 0); ; )
> +    {
> +        enabled = io_bitmap && test_bit(port, io_bitmap);
> +        if ( !enabled || !--size )
> +            break;
> +        if ( unlikely(++port == 8 * PAGE_SIZE) )
> +        {
> +            hvm_unmap_guest_frame(io_bitmap, 0);
> +            io_bitmap = hvm_map_guest_frame_ro(++gfn, 0);
> +            port -= 8 * PAGE_SIZE;
> +        }
>      }

Ok - this safe now, but I don't understand the reasoning for introducing
this loop?

The ioio exit value gives us a single port, and the size of access on
that specific port.

The switch statement tells us exactly which gfn the relevant bit refers
to, surely a single hvm_map_guest_frame_ro() is sufficient?

~Andrew

> -
> -    enabled = test_bit(port, io_bitmap);
>      hvm_unmap_guest_frame(io_bitmap, 0);
>  
> -    if (!enabled)
> +    if ( !enabled )
>          return NESTEDHVM_VMEXIT_HOST;
>  
>      return NESTEDHVM_VMEXIT_INJECT;
> @@ -966,8 +973,8 @@ nsvm_vmcb_guest_intercepts_exitcode(stru
>      switch (exitcode) {
>      case VMEXIT_MSR:
>          ASSERT(regs != NULL);
> -        nestedsvm_vmcb_map(v, nv->nv_vvmcxaddr);
> -        ASSERT(nv->nv_vvmcx != NULL);
> +        if ( !nestedsvm_vmcb_map(v, nv->nv_vvmcxaddr) )
> +            break;
>          ns_vmcb = nv->nv_vvmcx;
>          vmexits = nsvm_vmcb_guest_intercepts_msr(svm->ns_cached_msrpm,
>              regs->ecx, ns_vmcb->exitinfo1 != 0);
> @@ -975,8 +982,8 @@ nsvm_vmcb_guest_intercepts_exitcode(stru
>              return 0;
>          break;
>      case VMEXIT_IOIO:
> -        nestedsvm_vmcb_map(v, nv->nv_vvmcxaddr);
> -        ASSERT(nv->nv_vvmcx != NULL);
> +        if ( !nestedsvm_vmcb_map(v, nv->nv_vvmcxaddr) )
> +            break;
>          ns_vmcb = nv->nv_vvmcx;
>          vmexits = nsvm_vmcb_guest_intercepts_ioio(ns_vmcb->_iopm_base_pa,
>              ns_vmcb->exitinfo1);
>
>