[Xen-devel] [PATCH 7/7] xen/debug: WARN_ON when identity PFN has no _PAGE_IOMAP flag set.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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)

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

Reviewed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/Kconfig |    8 ++++++++
 arch/x86/xen/mmu.c   |   38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 5b54892..e4343fe 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 6164323..72ca435 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1013,6 +1013,41 @@ 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);
@@ -2423,6 +2458,9 @@ __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;
-- 
1.7.1


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