Re: [PATCH v2 3/3] tools/libxc: use superpages during restore of HVM guest

[Olaf Hering <olaf@aepfle.de>]

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On Wed, Aug 23, Olaf Hering wrote:

> The value of p2m_size does not represent the actual number of pages
> assigned to a domU. This info is stored in getdomaininfo.max_pages,
> which is currently not used by restore. I will see if using this value
> will avoid triggering the Over-allocation check.

This untested change ontop of this series (done with git diff -w -b
base..HEAD) does some accounting to avoid Over-allocation:

diff --git a/tools/libxc/xc_sr_common.h b/tools/libxc/xc_sr_common.h
index 26c45fdd6d..e0321ea224 100644
--- a/tools/libxc/xc_sr_common.h
+++ b/tools/libxc/xc_sr_common.h
@@ -234,6 +234,8 @@ struct xc_sr_context
 
             int send_back_fd;
             unsigned long p2m_size;
+            unsigned long max_pages;
+            unsigned long tot_pages;
             xc_hypercall_buffer_t dirty_bitmap_hbuf;
 
             /* From Image Header. */
@@ -375,6 +377,7 @@ static inline bool xc_sr_bitmap_resize(struct xc_sr_bitmap *bm, unsigned long bi
 static inline void xc_sr_bitmap_free(struct xc_sr_bitmap *bm)
 {
     free(bm->p);
+    bm->p = NULL;
 }
 
 static inline bool xc_sr_set_bit(unsigned long bit, struct xc_sr_bitmap *bm)
diff --git a/tools/libxc/xc_sr_restore.c b/tools/libxc/xc_sr_restore.c
index 1f9fe25b8f..eff24d3805 100644
--- a/tools/libxc/xc_sr_restore.c
+++ b/tools/libxc/xc_sr_restore.c
@@ -758,6 +758,9 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t dom,
         return -1;
     }
 
+    /* See xc_domain_getinfo */
+    ctx.restore.max_pages = ctx.dominfo.max_memkb >> (PAGE_SHIFT-10);
+    ctx.restore.tot_pages = ctx.dominfo.nr_pages;
     ctx.restore.p2m_size = nr_pfns;
 
     if ( ctx.dominfo.hvm )
diff --git a/tools/libxc/xc_sr_restore_x86_hvm.c b/tools/libxc/xc_sr_restore_x86_hvm.c
index 60454148db..f2932dafb7 100644
--- a/tools/libxc/xc_sr_restore_x86_hvm.c
+++ b/tools/libxc/xc_sr_restore_x86_hvm.c
@@ -278,7 +278,8 @@ static int pfn_set_allocated(struct xc_sr_context *ctx, xen_pfn_t pfn)
 static int x86_hvm_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
 {
     xc_interface *xch = ctx->xch;
-    bool success = false;
+    struct xc_sr_bitmap *bm;
+    bool success = false, do_sp;
     int rc = -1, done;
     unsigned int order;
     unsigned long i;
@@ -303,15 +304,18 @@ static int x86_hvm_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
         return -1;
     }
     DPRINTF("idx_1g %lu idx_2m %lu\n", idx_1g, idx_2m);
-    if (!xc_sr_test_and_set_bit(idx_1g, &ctx->x86_hvm.restore.attempted_1g)) {
+
+    bm = &ctx->x86_hvm.restore.attempted_1g;
     order = SUPERPAGE_1GB_SHIFT;
     count = 1UL << order;
+    do_sp = ctx->restore.tot_pages + count <= ctx->restore.max_pages;
+    if ( do_sp && !xc_sr_test_and_set_bit(idx_1g, bm) ) {
         base_pfn = (pfn >> order) << order;
         extnt = base_pfn;
         done = xc_domain_populate_physmap(xch, ctx->domid, 1, order, 0, &extnt);
         DPRINTF("1G base_pfn %" PRI_xen_pfn " done %d\n", base_pfn, done);
         if ( done > 0 ) {
-            struct xc_sr_bitmap *bm = &ctx->x86_hvm.restore.attempted_2m;
+            bm = &ctx->x86_hvm.restore.attempted_2m;
             success = true;
             stat_1g = done;
             for ( i = 0; i < (count >> SUPERPAGE_2MB_SHIFT); i++ )
@@ -319,9 +323,11 @@ static int x86_hvm_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
         }
     }
 
-    if (!xc_sr_test_and_set_bit(idx_2m, &ctx->x86_hvm.restore.attempted_2m)) {
+    bm = &ctx->x86_hvm.restore.attempted_2m;
     order = SUPERPAGE_2MB_SHIFT;
     count = 1UL << order;
+    do_sp = ctx->restore.tot_pages + count <= ctx->restore.max_pages;
+    if ( do_sp && !xc_sr_test_and_set_bit(idx_2m, bm) ) {
         base_pfn = (pfn >> order) << order;
         extnt = base_pfn;
         done = xc_domain_populate_physmap(xch, ctx->domid, 1, order, 0, &extnt);
@@ -344,6 +350,7 @@ static int x86_hvm_allocate_pfn(struct xc_sr_context *ctx, xen_pfn_t pfn)
     if ( success == true ) {
         do {
             count--;
+            ctx->restore.tot_pages++;
             rc = pfn_set_allocated(ctx, base_pfn + count);
             if ( rc )
                 break;
@@ -396,6 +403,7 @@ static int x86_hvm_populate_pfns(struct xc_sr_context *ctx, unsigned count,
                 PERROR("Failed to release pfn %" PRI_xen_pfn, min_pfn);
                 goto err;
             }
+            ctx->restore.tot_pages--;
         }
         min_pfn++;
     }

Olaf

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