[Xen-devel] [PATCH v2] x86/traps: Correct overly-general assertion introduced in c/s d5c251c

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The assertion about guest paging mode must only apply to guest pagefaults, as
should the later call to paging_fault().

This ASSERT() accidentally also trips if Xen takes a pagefault when in HVM
context, such as a copy_to_user() failure in the shadow pagetable code.

Merge the ASSERT() into the later paging_fault() callsite, prediating
everything on guest_mode() to start with.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>

v2:
 * Avoid calling paging_fault() for hypervisor pagefaults.
---
 xen/arch/x86/traps.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 2d79ee0..7f28d0a 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1797,10 +1797,6 @@ static int fixup_page_fault(unsigned long addr, struct 
cpu_user_regs *regs)
     if ( in_irq() || !(regs->eflags & X86_EFLAGS_IF) )
         return 0;
 
-    /* Logdirty mode is the only expected paging mode for PV guests. */
-    if ( paging_mode_enabled(d) )
-        ASSERT(paging_mode_only_log_dirty(d));
-
     if ( !(regs->error_code & PFEC_page_present) &&
           (pagefault_by_memadd(addr, regs)) )
         return handle_memadd_fault(addr, regs);
@@ -1831,10 +1827,17 @@ static int fixup_page_fault(unsigned long addr, struct 
cpu_user_regs *regs)
             return EXCRET_fault_fixed;
     }
 
-    /* Logdirty guests call back into the paging code to update shadows. */
-    if ( paging_mode_log_dirty(d) )
+    /*
+     * Logdirty guests call back into the paging code to update shadows.  We
+     * don't expect any other paging modes with PV guests.
+     */
+    if ( guest_mode(regs) && paging_mode_enabled(d) )
     {
-        int ret = paging_fault(addr, regs);
+        int ret;
+
+        ASSERT(paging_mode_only_log_dirty(d));
+
+        ret = paging_fault(addr, regs);
         if ( ret == EXCRET_fault_fixed )
             trace_trap_two_addr(TRC_PV_PAGING_FIXUP, regs->eip, addr);
         return ret;
-- 
2.1.4


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