[Xen-changelog] [qemu-upstream-unstable] xen/MSI-X: limit error messages

[patchbot@xxxxxxx]

commit 1f26a9bbce40a5f9651e1062a8ab9975e68d9f03
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 2 15:43:07 2015 +0000
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CommitDate: Tue Jun 9 10:28:24 2015 +0000

    xen/MSI-X: limit error messages
    
    Limit error messages resulting from bad guest behavior to avoid allowing
    the guest to cause the control domain's disk to fill.
    
    The first message in pci_msix_write() can simply be deleted, as this
    is indeed bad guest behavior, but such out of bounds writes don't
    really need to be logged.
    
    The second one is more problematic, as there guest behavior may only
    appear to be wrong: For one, the old logic didn't take the mask-all bit
    into account. And then this shouldn't depend on host device state (i.e.
    the host may have masked the entry without the guest having done so).
    Plus these writes shouldn't be dropped even when an entry is unmasked.
    Instead, if they can't be made take effect right away, they should take
    effect on the next unmasking or enabling operation - the specification
    explicitly describes such caching behavior. Until we can validly drop
    the message (implementing such caching/latching behavior), issue the
    message just once per MSI-X table entry.
    
    Note that the log message in pci_msix_read() similar to the one being
    removed here is not an issue: "addr" being of unsigned type, and the
    maximum size of the MSI-X table being 32k, entry_nr simply can't be
    negative and hence the conditonal guarding issuing of the message will
    never be true.
    
    This is XSA-130.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 hw/xen/xen_pt.h     |    1 +
 hw/xen/xen_pt_msi.c |   12 +++++++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/hw/xen/xen_pt.h b/hw/xen/xen_pt.h
index 52ceb85..8c9b6c2 100644
--- a/hw/xen/xen_pt.h
+++ b/hw/xen/xen_pt.h
@@ -175,6 +175,7 @@ typedef struct XenPTMSIXEntry {
     uint32_t data;
     uint32_t vector_ctrl;
     bool updated; /* indicate whether MSI ADDR or DATA is updated */
+    bool warned;  /* avoid issuing (bogus) warning more than once */
 } XenPTMSIXEntry;
 typedef struct XenPTMSIX {
     uint32_t ctrl_offset;
diff --git a/hw/xen/xen_pt_msi.c b/hw/xen/xen_pt_msi.c
index 9ed9321..68db623 100644
--- a/hw/xen/xen_pt_msi.c
+++ b/hw/xen/xen_pt_msi.c
@@ -434,11 +434,10 @@ static void pci_msix_write(void *opaque, hwaddr addr,
     XenPCIPassthroughState *s = opaque;
     XenPTMSIX *msix = s->msix;
     XenPTMSIXEntry *entry;
-    int entry_nr, offset;
+    unsigned int entry_nr, offset;
 
     entry_nr = addr / PCI_MSIX_ENTRY_SIZE;
-    if (entry_nr < 0 || entry_nr >= msix->total_entries) {
-        XEN_PT_ERR(&s->dev, "asked MSI-X entry '%i' invalid!\n", entry_nr);
+    if (entry_nr >= msix->total_entries) {
         return;
     }
     entry = &msix->msix_entry[entry_nr];
@@ -460,8 +459,11 @@ static void pci_msix_write(void *opaque, hwaddr addr,
             + PCI_MSIX_ENTRY_VECTOR_CTRL;
 
         if (msix->enabled && !(*vec_ctrl & PCI_MSIX_ENTRY_CTRL_MASKBIT)) {
-            XEN_PT_ERR(&s->dev, "Can't update msix entry %d since MSI-X is"
-                       " already enabled.\n", entry_nr);
+            if (!entry->warned) {
+                entry->warned = true;
+                XEN_PT_ERR(&s->dev, "Can't update msix entry %d since MSI-X is"
+                           " already enabled.\n", entry_nr);
+            }
             return;
         }
 
--
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

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