[xen staging] x86/vpci: fix handling of BAR overlaps with non-hole regions

[patchbot@xxxxxxx]

commit 4acab25a9300ba69a3c1441491470bd65af52d0f
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Mon May 12 17:05:38 2025 +0200
Commit:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
CommitDate: Wed May 21 18:29:55 2025 +0200

    x86/vpci: fix handling of BAR overlaps with non-hole regions
    
    For once the message printed when a BAR overlaps with a non-hole regions is
    not accurate on x86.  While the BAR won't be mapped by the vPCI logic, it
    is quite likely overlapping with a reserved region in the memory map, and
    already mapped as by default all reserved regions are identity mapped in
    the p2m.  Avoid printing the warning message in modify_bars(), and instead
    print a more lax message in the x86 implementation of pci_check_bar() to
    note the current BAR position overlaps with non-hole region(s).
    
    Secondly, when an overlap is detected the BAR 'enabled' field is not set,
    hence other vPCI code that depends on it like vPCI MSI-X handling won't
    function properly, as it sees the BAR as disabled, even when memory
    decoding is enabled for the device and the BAR is likely mapped in the
    p2m.  Change the handling of BARs that overlap non-hole regions to instead
    remove any overlapped regions from the rangeset, so the resulting ranges to
    map just contain the hole regions.  This requires introducing a new
    pci_sanitize_bar_memory() that's implemented per-arch and sanitizes the
    address range to add to the p2m.
    
    For x86 pci_sanitize_bar_memory() removes any regions present in the host
    memory map, for ARM this is currently left as a dummy handler to not change
    existing behavior.
    
    Ultimately the above changes should fix the vPCI MSI-X handlers not working
    correctly when the BAR that contains the MSI-X table overlaps with a
    non-hole region, as then the 'enabled' BAR bit won't be set and the MSI-X
    traps won't handle accesses as expected.
    
    Reported-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
    Fixes: 53d9133638c3 ('pci: do not disable memory decoding for devices')
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Tested-by: Victor M Lira <victorm.lira@xxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 xen/arch/arm/include/asm/pci.h |  3 +++
 xen/arch/x86/include/asm/pci.h | 13 ++++-------
 xen/arch/x86/pci.c             | 50 ++++++++++++++++++++++++++++++++++++++++++
 xen/drivers/vpci/header.c      |  9 ++++++++
 4 files changed, 66 insertions(+), 9 deletions(-)

diff --git a/xen/arch/arm/include/asm/pci.h b/xen/arch/arm/include/asm/pci.h
index 7f77226c9b..1605ec660d 100644
--- a/xen/arch/arm/include/asm/pci.h
+++ b/xen/arch/arm/include/asm/pci.h
@@ -128,6 +128,9 @@ int pci_host_bridge_mappings(struct domain *d);
 
 bool pci_check_bar(const struct pci_dev *pdev, mfn_t start, mfn_t end);
 
+static inline int pci_sanitize_bar_memory(struct rangeset *r)
+{ return 0; }
+
 #else   /*!CONFIG_HAS_PCI*/
 
 struct pci_dev;
diff --git a/xen/arch/x86/include/asm/pci.h b/xen/arch/x86/include/asm/pci.h
index fd5480d67d..bed99437cc 100644
--- a/xen/arch/x86/include/asm/pci.h
+++ b/xen/arch/x86/include/asm/pci.h
@@ -57,14 +57,9 @@ static always_inline bool is_pci_passthrough_enabled(void)
 
 void arch_pci_init_pdev(struct pci_dev *pdev);
 
-static inline bool pci_check_bar(const struct pci_dev *pdev,
-                                 mfn_t start, mfn_t end)
-{
-    /*
-     * Check if BAR is not overlapping with any memory region defined
-     * in the memory map.
-     */
-    return is_memory_hole(start, end);
-}
+bool pci_check_bar(const struct pci_dev *pdev, mfn_t start, mfn_t end);
+
+struct rangeset;
+int pci_sanitize_bar_memory(struct rangeset *r);
 
 #endif /* __X86_PCI_H__ */
diff --git a/xen/arch/x86/pci.c b/xen/arch/x86/pci.c
index 97b792e578..afaf9fe1c0 100644
--- a/xen/arch/x86/pci.c
+++ b/xen/arch/x86/pci.c
@@ -98,3 +98,53 @@ int pci_conf_write_intercept(unsigned int seg, unsigned int 
bdf,
 
     return rc;
 }
+
+bool pci_check_bar(const struct pci_dev *pdev, mfn_t start, mfn_t end)
+{
+    /*
+     * Check if BAR is not overlapping with any memory region defined
+     * in the memory map.
+     */
+    if ( !is_memory_hole(start, end) )
+        gdprintk(XENLOG_WARNING,
+                 "%pp: BAR at [%"PRI_mfn", %"PRI_mfn"] not in memory map 
hole\n",
+                 &pdev->sbdf, mfn_x(start), mfn_x(end));
+
+    /*
+     * Unconditionally return true, pci_sanitize_bar_memory() will remove any
+     * non-hole regions.
+     */
+    return true;
+}
+
+/* Remove overlaps with any ranges defined in the host memory map. */
+int pci_sanitize_bar_memory(struct rangeset *r)
+{
+    unsigned int i;
+
+    for ( i = 0; i < e820.nr_map; i++ )
+    {
+        const struct e820entry *entry = &e820.map[i];
+        int rc;
+
+        if ( !entry->size )
+            continue;
+
+        rc = rangeset_remove_range(r, PFN_DOWN(entry->addr),
+                                   PFN_UP(entry->addr + entry->size - 1));
+        if ( rc )
+            return rc;
+    }
+
+    return 0;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
index ef6c965c08..1f48f2aac6 100644
--- a/xen/drivers/vpci/header.c
+++ b/xen/drivers/vpci/header.c
@@ -394,6 +394,15 @@ static int modify_bars(const struct pci_dev *pdev, 
uint16_t cmd, bool rom_only)
                 return rc;
             }
         }
+
+        rc = pci_sanitize_bar_memory(bar->mem);
+        if ( rc )
+        {
+            gprintk(XENLOG_WARNING,
+                    "%pp: failed to sanitize BAR#%u memory: %d\n",
+                    &pdev->sbdf, i, rc);
+            return rc;
+        }
     }
 
     /* Remove any MSIX regions if present. */
--
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