[xen staging] x86/cpu: populate CPUID 0x1.edx features early for self-snoop detection

[patchbot@xxxxxxx]

commit 382dd0d166cb85139d86ff26fd96af102ae4fef3
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Sep 24 09:59:46 2025 +0200
Commit:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
CommitDate: Thu Sep 25 16:07:05 2025 +0200

    x86/cpu: populate CPUID 0x1.edx features early for self-snoop detection
    
    Otherwise the check for the SS feature in
    check_memory_type_self_snoop_errata() fails unconditionally, which leads to
    X86_FEATURE_XEN_SELFSNOOP never being set.
    
    We could also avoid this by not doing the reset_cpuinfo() for the BSP in
    identify_cpu(), because SS detection uses boot_cpu_data.  However that
    creates an imbalance on the state of the BSP versus the APs in the
    identify_cpu() code.
    
    I've opted for the less controversial solution of populating FEATURESET_1d
    in generic_identify(), as the value is already there.  The same is done for
    the AMD faulting probe code.  While there also populate the FEATURESET_1c
    element, as the value is in context.
    
    Fixes: f2663ca2e520 ("x86/cpu/intel: Clear cache self-snoop capability in 
CPUs with known errata")
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu/common.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 530b9eb39a..8c8bf1a806 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -490,6 +490,13 @@ static void generic_identify(struct cpuinfo_x86 *c)
        c->apicid = phys_pkg_id((ebx >> 24) & 0xFF, 0);
        c->phys_proc_id = c->apicid;
 
+       /*
+        * Early init of Self Snoop support requires 0x1.edx, while there also
+        * set 0x1.ecx as the value is in context.
+        */
+       c->x86_capability[FEATURESET_1c] = ecx;
+       c->x86_capability[FEATURESET_1d] = edx;
+
        eax = cpuid_eax(0x80000000);
        if ((eax >> 16) == 0x8000)
                c->extended_cpuid_level = eax;
--
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