RE: [Xen-devel] [PATCH] supporting non-NX/XD capable processors on x86_64 xenlinux

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Keir Fraser wrote:
> On 18 Aug 2005, at 05:29, Nakajima, Jun wrote:
> 
>> I don't have particular preference, but the latter one's change is
>> smaller, and it can fix other places (that are using the attrributes
>> derived from __PAGE_KERNEL). But the former one is cleaner to me. If
>> people agree, I can make such a patch.
> 
> How does native x86/64 Linux avoid this problem? It doesn't mask
> __PAGE_KERNEL with __supported_pte_mask, so I'm reluctant to take this
> patch. Seems to me there is some other underlying difference between
> us and native that is not best solved by diverging even further.
> 
> Unless native doesn;t boot on these failing boxes either?
> 
>   -- Keir

One obvious reason is: xen-specific drivers are using __PAGE_KERNEL (and
they don't exist in the native Linux). If xen_contig_memory, for
example, does not work, it won't boot... Fixing xen_contig_memory did
not fix the booting problem as long as I remember? Since then we fixed
some attribute problems in other xen-specific drivers when we brough up
domU, so I'll take a look.

xen_contig_memory
...
    /* 3. Map the new extent in place of old pages. */
    for (i = 0; i < (1<<order); i++) {
        BUG_ON(HYPERVISOR_update_va_mapping(
            vstart + (i*PAGE_SIZE),
            __pte_ma(((mfn+i)<<PAGE_SHIFT)|__PAGE_KERNEL), 0));
        xen_machphys_update(mfn+i, (__pa(vstart)>>PAGE_SHIFT)+i);
        phys_to_machine_mapping[(__pa(vstart)>>PAGE_SHIFT)+i] = mfn+i;
    }


blkback.c:  dispatch_probe
static void dispatch_probe(blkif_t *blkif, blkif_request_t *req)
{
 ...
#ifdef CONFIG_XEN_BLKDEV_TAP_BE
    if ( HYPERVISOR_update_va_mapping_otherdomain(
        MMAP_VADDR(pending_idx, 0),
        (pte_t) { (req->frame_and_sects[0] & PAGE_MASK) | __PAGE_KERNEL
},
        0, (blkif->is_blktap ? ID_TO_DOM(req->id) : blkif->domid) ) )

        goto out;
#else
    if ( HYPERVISOR_update_va_mapping_otherdomain(
        MMAP_VADDR(pending_idx, 0),
        (pte_t) { (req->frame_and_sects[0] & PAGE_MASK) | __PAGE_KERNEL
},
        0, blkif->domid) )

        goto out;
#endif
#endif /* endif CONFIG_XEN_BLKDEV_GRANT */

Jun
---
Intel Open Source Technology Center

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