[xen staging] x86/PCI: avoid re-evaluation of extended config space accessibility

[patchbot@xxxxxxx]

commit d96694508a2867726162941f163400368a07c91b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Feb 11 09:21:35 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 11 09:21:35 2026 +0100

    x86/PCI: avoid re-evaluation of extended config space accessibility
    
    When, during boot, we have already correctly determined availability of
    the MMCFG access method for a given bus range, there's then no need to
    invoke pci_check_extcfg() again for every of the devices. This in
    particular avoids ->ext_cfg to transiently indicate the wrong state.
    
    Switch to using Xen style on lines being touched and immediately adjacent
    ones.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
---
 xen/arch/x86/physdev.c                |  2 ++
 xen/arch/x86/x86_64/mmconfig-shared.c | 16 +++++++++-------
 xen/arch/x86/x86_64/mmconfig.h        |  2 +-
 xen/arch/x86/x86_64/mmconfig_64.c     | 10 +++++++---
 4 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
index f6014e2f49..8496011b59 100644
--- a/xen/arch/x86/physdev.c
+++ b/xen/arch/x86/physdev.c
@@ -528,6 +528,8 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
arg)
         if ( !ret )
             ret = pci_segment_iterate(info.segment, physdev_check_pci_extcfg,
                                       &info);
+        else if ( ret > 0 ) /* Indication of "no change". */
+            ret = 0;
 
         if ( !ret && has_vpci(currd) && (info.flags & XEN_PCI_MMCFG_RESERVED) )
         {
diff --git a/xen/arch/x86/x86_64/mmconfig-shared.c 
b/xen/arch/x86/x86_64/mmconfig-shared.c
index d53da1e2a7..ab082b5f5b 100644
--- a/xen/arch/x86/x86_64/mmconfig-shared.c
+++ b/xen/arch/x86/x86_64/mmconfig-shared.c
@@ -388,8 +388,9 @@ static bool __init pci_mmcfg_reject_broken(void)
                (unsigned int)cfg->start_bus_number,
                (unsigned int)cfg->end_bus_number);
 
-        if (!is_mmconf_reserved(addr, size, i, cfg) ||
-            pci_mmcfg_arch_enable(i)) {
+        if ( !is_mmconf_reserved(addr, size, i, cfg) ||
+             pci_mmcfg_arch_enable(i) < 0 )
+        {
             pci_mmcfg_arch_disable(i);
             valid = 0;
         }
@@ -417,8 +418,8 @@ void __init acpi_mmcfg_init(void)
         unsigned int i;
 
         pci_mmcfg_arch_init();
-        for (i = 0; i < pci_mmcfg_config_num; ++i)
-            if (pci_mmcfg_arch_enable(i))
+        for ( i = 0; i < pci_mmcfg_config_num; ++i )
+            if ( pci_mmcfg_arch_enable(i) < 0 )
                 valid = 0;
     } else {
         acpi_table_parse(ACPI_SIG_MCFG, acpi_parse_mcfg);
@@ -458,10 +459,11 @@ int pci_mmcfg_reserved(uint64_t address, unsigned int 
segment,
                        segment, start_bus, end_bus, address, cfg->address);
                 return -EIO;
             }
-            if (flags & XEN_PCI_MMCFG_RESERVED)
+
+            if ( flags & XEN_PCI_MMCFG_RESERVED )
                 return pci_mmcfg_arch_enable(i);
-            pci_mmcfg_arch_disable(i);
-            return 0;
+
+            return pci_mmcfg_arch_disable(i);
         }
     }
 
diff --git a/xen/arch/x86/x86_64/mmconfig.h b/xen/arch/x86/x86_64/mmconfig.h
index 722bf67975..27c0ae5cb1 100644
--- a/xen/arch/x86/x86_64/mmconfig.h
+++ b/xen/arch/x86/x86_64/mmconfig.h
@@ -74,6 +74,6 @@ int pci_mmcfg_reserved(uint64_t address, unsigned int segment,
                        unsigned int flags);
 int pci_mmcfg_arch_init(void);
 int pci_mmcfg_arch_enable(unsigned int idx);
-void pci_mmcfg_arch_disable(unsigned int idx);
+int pci_mmcfg_arch_disable(unsigned int idx);
 
 #endif /* X86_64_MMCONFIG_H */
diff --git a/xen/arch/x86/x86_64/mmconfig_64.c 
b/xen/arch/x86/x86_64/mmconfig_64.c
index ffdc62700d..940cf6d747 100644
--- a/xen/arch/x86/x86_64/mmconfig_64.c
+++ b/xen/arch/x86/x86_64/mmconfig_64.c
@@ -138,8 +138,9 @@ int pci_mmcfg_arch_enable(unsigned int idx)
     const typeof(pci_mmcfg_config[0]) *cfg = pci_mmcfg_virt[idx].cfg;
     unsigned long start_mfn, end_mfn;
 
-    if (pci_mmcfg_virt[idx].virt)
-        return 0;
+    if ( pci_mmcfg_virt[idx].virt )
+        return 1;
+
     pci_mmcfg_virt[idx].virt = mcfg_ioremap(cfg, idx, PAGE_HYPERVISOR_UC);
     if (!pci_mmcfg_virt[idx].virt) {
         printk(KERN_ERR "PCI: Cannot map MCFG aperture for segment %04x\n",
@@ -160,9 +161,10 @@ int pci_mmcfg_arch_enable(unsigned int idx)
     return 0;
 }
 
-void pci_mmcfg_arch_disable(unsigned int idx)
+int pci_mmcfg_arch_disable(unsigned int idx)
 {
     const typeof(pci_mmcfg_config[0]) *cfg = pci_mmcfg_virt[idx].cfg;
+    int ret = !pci_mmcfg_virt[idx].virt;
 
     pci_mmcfg_virt[idx].virt = NULL;
     /*
@@ -173,6 +175,8 @@ void pci_mmcfg_arch_disable(unsigned int idx)
     mcfg_ioremap(cfg, idx, 0);
     printk(KERN_WARNING "PCI: Not using MCFG for segment %04x bus %02x-%02x\n",
            cfg->pci_segment, cfg->start_bus_number, cfg->end_bus_number);
+
+    return ret;
 }
 
 bool pci_mmcfg_decode(unsigned long mfn, unsigned int *seg, unsigned int *bdf)
--
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