[xen staging] x86/ioapic: Fix fixmap error path logic in ioapic_init_mappings()

[patchbot@xxxxxxx]

commit b4175c6693e089ffcd77cd1ea388e76e67d36d57
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Aug 5 12:05:27 2020 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Aug 5 17:35:11 2020 +0100

    x86/ioapic: Fix fixmap error path logic in ioapic_init_mappings()
    
    In the case that bad_ioapic_register() fails, the current position of idx++
    means that clear_fixmap(idx) will be called with the wrong index, and not
    clean up the mapping just created.
    
    Increment idx as part of the loop, rather than midway through the loop body.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/io_apic.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index 878ee5192d..e66fa99ec7 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -2543,7 +2543,7 @@ static void __init ioapic_init_mappings(void)
 
     nr_irqs_gsi = 0;
 
-    for ( i = 0; i < nr_ioapics; i++ )
+    for ( i = 0; i < nr_ioapics; i++, idx++ )
     {
         union IO_APIC_reg_01 reg_01;
         paddr_t ioapic_phys = mp_ioapics[i].mpc_apicaddr;
@@ -2560,7 +2560,6 @@ static void __init ioapic_init_mappings(void)
         set_fixmap_nocache(idx, ioapic_phys);
         apic_printk(APIC_VERBOSE, "mapped IOAPIC to %08Lx (%08lx)\n",
                     __fix_to_virt(idx), ioapic_phys);
-        idx++;
 
         if ( bad_ioapic_register(i) )
         {
--
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