xen/debug: WARN_ON when identity PFN has no _PAGE_IOMAP flag set.

Only enabled if XEN_DEBUG is enabled. We print a warning
when:

 pfn_to_mfn(pfn) == pfn, but no VM_IO (_PAGE_IOMAP) flag set
	(and pfn is an identity mapped pfn)
 pfn_to_mfn(pfn) != pfn, and VM_IO flag is set.
	(ditto, pfn is an identity mapped pfn)

[v2: Make it dependent on CONFIG_XEN_DEBUG instead of ..DEBUG_FS]
[v3: Fix compiler warning]

Reviewed-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

2 files changed, 46 insertions, 0 deletions

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 5b54892e4bc3..e4343fe488ed 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -48,3 +48,11 @@ config XEN_DEBUG_FS
         help
           Enable statistics output and various tuning options in debugfs.
           Enabling this option may incur a significant performance overhead.
+
+config XEN_DEBUG
+        bool "Enable Xen debug checks"
+        depends on XEN
+        default n
+        help
+          Enable various WARN_ON checks in the Xen MMU code.
+          Enabling this option WILL incur a significant performance overhead.
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index b13b6ca9052a..0c376a2d9f98 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -547,6 +547,41 @@ pte_t xen_make_pte(pteval_t pte)
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte);
 
+#ifdef CONFIG_XEN_DEBUG
+pte_t xen_make_pte_debug(pteval_t pte)
+{
+        phys_addr_t addr = (pte & PTE_PFN_MASK);
+        phys_addr_t other_addr;
+        bool io_page = false;
+        pte_t _pte;
+
+        if (pte & _PAGE_IOMAP)
+                io_page = true;
+
+        _pte = xen_make_pte(pte);
+
+        if (!addr)
+                return _pte;
+
+        if (io_page &&
+            (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
+                other_addr = pfn_to_mfn(addr >> PAGE_SHIFT) << PAGE_SHIFT;
+                WARN(addr != other_addr,
+                        "0x%lx is using VM_IO, but it is 0x%lx!\n",
+                        (unsigned long)addr, (unsigned long)other_addr);
+        } else {
+                pteval_t iomap_set = (_pte.pte & PTE_FLAGS_MASK) & _PAGE_IOMAP;
+                other_addr = (_pte.pte & PTE_PFN_MASK);
+                WARN((addr == other_addr) && (!io_page) && (!iomap_set),
+                        "0x%lx is missing VM_IO (and wasn't fixed)!\n",
+                        (unsigned long)addr);
+        }
+
+        return _pte;
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte_debug);
+#endif
+
 pgd_t xen_make_pgd(pgdval_t pgd)
 {
         pgd = pte_pfn_to_mfn(pgd);
@@ -1957,6 +1992,9 @@ __init void xen_ident_map_ISA(void)
 
 static __init void xen_post_allocator_init(void)
 {
+#ifdef CONFIG_XEN_DEBUG
+        pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte_debug);
+#endif
         pv_mmu_ops.set_pte = xen_set_pte;
         pv_mmu_ops.set_pmd = xen_set_pmd;
         pv_mmu_ops.set_pud = xen_set_pud;