[Xen-devel] Correctly mapping in a Dom0 page globally

[Bread Cutter <cutter409@xxxxxxxxx>]

Hello all,

I'm mapping in some memory from Dom0 to use globally, based on a
domctl that sends up a virtual address. It seems to be working for me
so far.

Here's my current code
----------------
{
    struct page_info* page_info = NULL;
    l1_pgentry_t pte;

    /* Attempt to read the PTE that maps the VA being accessed. */
    guest_get_eff_l1e(current, va, &pte);

    /* Make sure the page is present */
    if ( ((l1e_get_flags(pte) & (_PAGE_PRESENT)) != _PAGE_PRESENT) )
    {
        ret = -ENOMEM;
        break;
    }

    /* Get the page_info struct */
    page_info = l1e_get_page(pte);
    if ( !page_info )
    {
        ret = -ESRCH;
        break;
   }

    d->arch.hvm_domain.test.buffer =
(uint8_t*)__map_domain_page_global(page_info);
    if ( !d->arch.hvm_domain.test.buffer )
    {
        ret = -ESRCH;
        break;
    }
----------------

In the unmap function, I simply call
"map_domain_page_global(d->arch.hvm_domain.test.buffer)"

My concern is that I'm not actually calling get_page()/put_page().
The function "l1e_get_page()" seems to always succeed, but simply does
some math to find the structure. It doesn't end up calling get_page()
and incrementing the reference count.

My question is, am I doing this correctly? Will l1e_get_page() always
succeed? I was having issues getting get_page() and put_page() to work
using the pte.

Any comments will be greatly appreciated.

Thanks!

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