On 4/4/19 3:46 PM, Razvan Cojocaru wrote:
On 4/3/19 6:30 PM, Jan Beulich wrote:
On 03.04.19 at 17:17, <rcojoc...@bitdefender.com> wrote:
On 4/3/19 5:58 PM, Jan Beulich wrote:
On 03.04.19 at 16:29, <aisa...@bitdefender.com> wrote:
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -3011,8 +3011,16 @@ int p2m_set_suppress_ve(struct domain *d,
gfn_t gfn, bool suppress_ve,
mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, NULL, NULL);
if ( !mfn_valid(mfn) )
{
- rc = -ESRCH;
- goto out;
+ unsigned int page_order;
+
+ mfn = __get_gfn_type_access(host_p2m, gfn_x(gfn), &t, &a,
+ P2M_ALLOC | P2M_UNSHARE,
&page_order, 0);
I'm not entirely certain about P2M_ALLOC, but I'm pretty sure that
at least P2M_UNSHARE is too heavy: Why would you want to force
un-sharing of a page when all you want to alter is #VE behavior?
That logic was taken from p2m_set_altp2m_mem_access(), we thought the
two cases are very similar.
I see.
On the UNSHARE observation, we don't know why the author originally
requested the flag. We decided to keep it on the assumption that it
_probably_ handles some corner-case that somebody has come accross.
We'll prepare a mini-series factoring out the code we've been discussing
in separate functions: one for getting things out of the hostp2m if the
entry is not present in the altp2m, and one for the special
page-order-dependent code (which is duplicated in
p2m_set_altp2m_mem_access() and p2m_change_altp2m_gfn()).
Before going into that, are we now certain that ALLOC is sufficient? I
believe it should be for _our_ use-cases, but we don't want to break
anyone's code. Maybe Tamas knows more about this.
Sorry, I forgot to mention that p2m_change_altp2m_gfn() only uses ALLOC:
2649 /* Check host p2m if no valid entry in alternate */
2650 if ( !mfn_valid(mfn) )
2651 {
2652 mfn = __get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
2653 P2M_ALLOC, &page_order, 0);
2654
2655 if ( !mfn_valid(mfn) || t != p2m_ram_rw )
2656 goto out;
2657
2658 /* If this is a superpage, copy that first */
2659 if ( page_order != PAGE_ORDER_4K )
2660 {
2661 gfn_t gfn;
2662 unsigned long mask;
2663
2664 mask = ~((1UL << page_order) - 1);
2665 gfn = _gfn(gfn_x(old_gfn) & mask);
2666 mfn = _mfn(mfn_x(mfn) & mask);
2667
2668 if ( ap2m->set_entry(ap2m, gfn, mfn, page_order, t, a, 1) )
2669 goto out;
2670 }
2671 }
Confusing...
Thanks,
Razvan
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