Re: [PATCH v4 02/14] libxc: Prepare a start info structure for hvmloader

[Anthony PERARD <anthony.perard@citrix.com>]

> > diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
> > index bdec40a..9c56d55 100644
> > --- a/tools/libxc/xc_dom_x86.c
> > +++ b/tools/libxc/xc_dom_x86.c
> > @@ -69,6 +69,9 @@
> >  #define round_up(addr, mask)     ((addr) | (mask))
> >  #define round_pg_up(addr)  (((addr) + PAGE_SIZE_X86 - 1) & ~(PAGE_SIZE_X86 - 1))
> >  
> > +#define HVMLOADER_MODULE_MAX_COUNT 1
> > +#define HVMLOADER_MODULE_NAME_SIZE 10
> > +
> >  struct xc_dom_params {
> >      unsigned levels;
> >      xen_vaddr_t vaddr_mask;
> > @@ -590,6 +593,7 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
> >      xen_pfn_t special_array[X86_HVM_NR_SPECIAL_PAGES];
> >      xen_pfn_t ioreq_server_array[NR_IOREQ_SERVER_PAGES];
> >      xc_interface *xch = dom->xch;
> > +    size_t start_info_size = sizeof(struct hvm_start_info);
> >  
> >      /* Allocate and clear special pages. */
> >      for ( i = 0; i < X86_HVM_NR_SPECIAL_PAGES; i++ )
> > @@ -624,8 +628,6 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
> >  
> >      if ( !dom->device_model )
> >      {
> > -        size_t start_info_size = sizeof(struct hvm_start_info);
> > -
> >          if ( dom->cmdline )
> >          {
> >              dom->cmdline_size = ROUNDUP(strlen(dom->cmdline) + 1, 8);
> > @@ -635,17 +637,26 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
> >          /* Limited to one module. */
> >          if ( dom->ramdisk_blob )
> >              start_info_size += sizeof(struct hvm_modlist_entry);
> > -
> > -        rc = xc_dom_alloc_segment(dom, &dom->start_info_seg,
> > -                                  "HVMlite start info", 0, start_info_size);
> > -        if ( rc != 0 )
> > -        {
> > -            DOMPRINTF("Unable to reserve memory for the start info");
> > -            goto out;
> > -        }
> >      }
> >      else
> >      {
> > +        start_info_size +=
> > +            sizeof(struct hvm_modlist_entry) * HVMLOADER_MODULE_MAX_COUNT;
> > +        /* Add extra space to write modules name */
> > +        start_info_size +=
> > +            HVMLOADER_MODULE_NAME_SIZE * HVMLOADER_MODULE_MAX_COUNT;
> 
> What about \0 ? Ah, the strncpy we use adds \0 byte. But it would be nice
> to mention that somewhere. Perhaps mention:
> 
> The HVMLOADER_MODULE_NAME_SIZE accounts for NUL byte?

Yes, I can add a comment about it.

> > +    }
> > +
> > +    rc = xc_dom_alloc_segment(dom, &dom->start_info_seg,
> > +                              "HVMlite start info", 0, start_info_size);
> > +    if ( rc != 0 )
> > +    {
> > +        DOMPRINTF("Unable to reserve memory for the start info");
> > +        goto out;
> > +    }
> > +
> > +    if ( dom->device_model )
> > +    {
> >          /*
> >           * Allocate and clear additional ioreq server pages. The default
> >           * server will use the IOREQ and BUFIOREQ special pages above.
> > @@ -1696,39 +1707,68 @@ static int alloc_pgtables_hvm(struct xc_dom_image *dom)
> >      return 0;
> >  }
> >  
> > +static void add_module_to_list(struct xc_dom_image *dom,
> > +                               struct xc_hvm_firmware_module *module,
> > +                               const char *name,
> > +                               struct hvm_modlist_entry *modlist,
> > +                               struct hvm_start_info *start_info)
> > +{
> > +    uint32_t index = start_info->nr_modules;
> > +    if ( module->length == 0 )
> > +        return;
> > +
> > +    assert(start_info->nr_modules < HVMLOADER_MODULE_MAX_COUNT);
> > +    assert(strnlen(name, HVMLOADER_MODULE_NAME_SIZE)
> > +           < HVMLOADER_MODULE_NAME_SIZE);
> > +
> > +    modlist[index].paddr = module->guest_addr_out;
> > +    modlist[index].size = module->length;
> > +    strncpy((char*)(modlist + HVMLOADER_MODULE_MAX_COUNT)
> > +            + HVMLOADER_MODULE_NAME_SIZE * index,
> > +            name, HVMLOADER_MODULE_NAME_SIZE);
> > +    modlist[index].cmdline_paddr =
> > +        (dom->start_info_seg.pfn << PAGE_SHIFT) +
> > +        ((uintptr_t)modlist - (uintptr_t)start_info) +
> > +        sizeof(struct hvm_modlist_entry) * HVMLOADER_MODULE_MAX_COUNT +
> > +        HVMLOADER_MODULE_NAME_SIZE * index;
> 
> That looks right, but boy it takes a bit of thinking to
> make sure it is right. Perhaps put a comment outlining where
> it ought to be (so folks reading the first time can feel
> OK they got it right?)

Yes, I can add comments, and maybe try to simplify it a bit.

-- 
Anthony PERARD

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