[PATCH 02/11] xen/page_alloc: Remove `claim` from domain_set_outstanding_pages()

[Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>]

With a single global count for the claims it's easy to substract
domain_tot_pages() from the claim so the number given in the hypercall
is the real reservation of the domain. This is the current behaviour.

However, a later patch introduces exact-node claims and those interact
very poorly with such a scheme. Since accounting domain_tot_pages() in
one case but not the other seems strictly worse than not accounting them
at all (which is at least consistent), this patch stops substracting
tot_pages from the claim and instead checks that claimed memory +
allocated memory don't exceed max_mem.

Arguably it's also clearer for the caller to align the amount of claimed
memory with that of the requested claim.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
---
 xen/common/page_alloc.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index bd4538c28d82..49c3258169db 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -523,7 +523,7 @@ out:
 int domain_set_outstanding_pages(struct domain *d, unsigned long pages)
 {
     int ret = -ENOMEM;
-    unsigned long claim, avail_pages;
+    unsigned long avail_pages;
 
     /*
      * take the domain's page_alloc_lock, else all d->tot_page adjustments
@@ -549,28 +549,21 @@ int domain_set_outstanding_pages(struct domain *d, 
unsigned long pages)
         goto out;
     }
 
-    /* disallow a claim not exceeding domain_tot_pages() or above max_pages */
-    if ( (pages <= domain_tot_pages(d)) || (pages > d->max_pages) )
+    /* Don't claim past max_pages */
+    if ( (domain_tot_pages(d) + pages) > d->max_pages )
     {
         ret = -EINVAL;
         goto out;
     }
 
     /* how much memory is available? */
-    avail_pages = total_avail_pages;
+    avail_pages = total_avail_pages - outstanding_claims;
 
-    avail_pages -= outstanding_claims;
-
-    /*
-     * Note, if domain has already allocated memory before making a claim
-     * then the claim must take domain_tot_pages() into account
-     */
-    claim = pages - domain_tot_pages(d);
-    if ( claim > avail_pages )
+    if ( pages > avail_pages )
         goto out;
 
     /* yay, claim fits in available memory, stake the claim, success! */
-    d->outstanding_pages = claim;
+    d->outstanding_pages = pages;
     outstanding_claims += d->outstanding_pages;
     ret = 0;
 
-- 
2.48.1