[xen stable-4.20] x86/idle: Fix the C6 eoi_errata[] list to include NEHALEM_EX

[patchbot@xxxxxxx]

commit 73eaac394c3163a7d1b888911a2457edd467b2c5
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jul 22 09:55:07 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jul 22 09:55:07 2025 +0200

    x86/idle: Fix the C6 eoi_errata[] list to include NEHALEM_EX
    
    NEHALEM_EX is affected by the erratum too.
    
    Change the comment to be the full erratum text, not an interpretation of it.
    
    Fixes: 95807bcae47e ("C6 state with EOI issue fix for some Intel 
processors")
    Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: d225205a0b85b748151ebd880ee29dad55cb0a15
    master date: 2025-07-18 13:40:12 +0100
---
 xen/arch/x86/acpi/cpu_idle.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index 24447fb933..914661312d 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -584,18 +584,24 @@ bool errata_c6_workaround(void)
     {
 #define INTEL_FAM6_MODEL(m) { X86_VENDOR_INTEL, 6, m, X86_FEATURE_ALWAYS }
         /*
-         * Errata AAJ72: EOI Transaction May Not be Sent if Software Enters
-         * Core C6 During an Interrupt Service Routine"
+         * Errata AAJ72, etc: EOI Transaction May Not be Sent if Software
+         * Enters Core C6 During an Interrupt Service Routine
          *
-         * There was an errata with some Core i7 processors that an EOI
-         * transaction may not be sent if software enters core C6 during an
-         * interrupt service routine. So we don't enter deep Cx state if
-         * there is an EOI pending.
+         * If core C6 is entered after the start of an interrupt service
+         * routine but before a write to the APIC EOI (End of Interrupt)
+         * register, and the core is woken up by an event other than a fixed
+         * interrupt source the core may drop the EOI transaction the next
+         * time APIC EOI register is written and further interrupts from the
+         * same or lower priority level will be blocked.
+         *
+         * Software should check the ISR register and if any interrupts are in
+         * service only enter C1.
          */
         static const struct x86_cpu_id eoi_errata[] = {
-            INTEL_FAM6_MODEL(0x1a),
+            INTEL_FAM6_MODEL(0x1a), /* AAJ72 */
             INTEL_FAM6_MODEL(0x1e),
             INTEL_FAM6_MODEL(0x1f),
+            INTEL_FAM6_MODEL(0x2e), /* BA106 */
             INTEL_FAM6_MODEL(0x25),
             INTEL_FAM6_MODEL(0x2c),
             INTEL_FAM6_MODEL(0x2f),
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.20