[xen master] x86/cpu: revert opt_allow_unsafe from __ro_after_init to __read_mostly

[patchbot@xxxxxxx]

commit 1e6bb29b03680a9d0e12f14c4d406a0d67317ea7
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Sep 2 17:34:54 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 2 17:34:54 2024 +0200

    x86/cpu: revert opt_allow_unsafe from __ro_after_init to __read_mostly
    
    Making opt_allow_unsafe read only after init requires changes to the logic 
in
    init_amd(), otherwise the following #PF happens on CPU hotplug:
    
    ----[ Xen-4.20.0-1-d  x86_64  debug=y  Tainted:     H  ]----
    CPU:    1
    RIP:    e008:[<ffff82d040291081>] arch/x86/cpu/amd.c#init_amd+0x37f/0x993
    [...]
    Xen call trace:
       [<ffff82d040291081>] R arch/x86/cpu/amd.c#init_amd+0x37f/0x993
       [<ffff82d040291fbe>] F identify_cpu+0x2d4/0x4db
       [<ffff82d04032eeaa>] F start_secondary+0x22e/0x3cf
       [<ffff82d040203327>] F __high_start+0x87/0xa0
    
    Pagetable walk from ffff82d0404011ea:
     L4[0x105] = 000000006fc2e063 ffffffffffffffff
     L3[0x141] = 000000006fc2b063 ffffffffffffffff
     L2[0x002] = 000000807c7ca063 ffffffffffffffff
     L1[0x001] = 800000006f801121 ffffffffffffffff
    
    ****************************************
    Panic on CPU 1:
    FATAL PAGE FAULT
    [error_code=0003]
    Faulting linear address: ffff82d0404011ea
    ****************************************
    
    For the time being revert opt_allow_unsafe to be __read_mostly.
    
    Fixes: bfcb0abb191f ('types: replace remaining uses of s8')
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu/amd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 903be14af4..7da0423039 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -46,7 +46,7 @@ static unsigned int __initdata opt_cpuid_mask_thermal_ecx = 
~0u;
 integer_param("cpuid_mask_thermal_ecx", opt_cpuid_mask_thermal_ecx);
 
 /* 1 = allow, 0 = don't allow guest creation, -1 = don't allow boot */
-int8_t __ro_after_init opt_allow_unsafe;
+int8_t __read_mostly opt_allow_unsafe;
 boolean_param("allow_unsafe", opt_allow_unsafe);
 
 /* Signal whether the ACPI C1E quirk is required. */
--
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