[Xen-changelog] [xen master] x86/smp: do not use scratch_cpumask when in interrupt or exception context

[patchbot@xxxxxxx]

commit d079cc05873904c855bf2fb4d8db72fbb3727c9d
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Feb 26 17:38:58 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 26 17:38:58 2020 +0100

    x86/smp: do not use scratch_cpumask when in interrupt or exception context
    
    Using scratch_cpumask in send_IPI_mask is not safe in IRQ or exception
    context because it can nest, and hence send_IPI_mask could be
    overwriting another user scratch cpumask data when used in such
    contexts.
    
    Fallback to not using the scratch cpumask (and hence not attemping to
    optimize IPI sending by using a shorthand) when in IRQ or exception
    context. Note that the scratch cpumask cannot be used when
    non-maskable interrupts are being serviced (NMI or #MC) and hence
    fallback to not using the shorthand in that case, like it was done
    previously.
    
    Fixes: 5500d265a2a8 ('x86/smp: use APIC ALLBUT destination shorthand when 
possible')
    Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/smp.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xen/arch/x86/smp.c b/xen/arch/x86/smp.c
index fac295fa6f..a90c782d53 100644
--- a/xen/arch/x86/smp.c
+++ b/xen/arch/x86/smp.c
@@ -68,6 +68,18 @@ void send_IPI_mask(const cpumask_t *mask, int vector)
     bool cpus_locked = false;
     cpumask_t *scratch = this_cpu(scratch_cpumask);
 
+    if ( in_irq() || in_mce_handler() || in_nmi_handler() )
+    {
+        /*
+         * When in IRQ, NMI or #MC context fallback to the old (and simpler)
+         * IPI sending routine, and avoid doing any performance optimizations
+         * (like using a shorthand) in order to avoid using the scratch
+         * cpumask which cannot be used in interrupt context.
+         */
+        alternative_vcall(genapic.send_IPI_mask, mask, vector);
+        return;
+    }
+
     /*
      * This can only be safely used when no CPU hotplug or unplug operations
      * are taking place, there are no offline CPUs (unless those have been
--
generated by git-patchbot for /home/xen/git/xen.git#master

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/xen-changelog