[xen staging] x86/traps: Rework LER initialisation and support Zen5/Diamond Rapids

[patchbot@xxxxxxx]

commit 555866cb56002849014a1409ecdfa3f436c0c2c4
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Dec 31 14:06:19 2024 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Jan 6 12:24:05 2025 +0000

    x86/traps: Rework LER initialisation and support Zen5/Diamond Rapids
    
    AMD have always used the architectural MSRs for LER.  As the first processor
    to support LER was the K7 (which was 32bit), we can assume it's presence
    unconditionally in 64bit mode.
    
    Intel are about to run out of space in Family 6 and start using 19.  It is
    only the Pentium 4 which uses non-architectural LER MSRs.
    
    percpu_traps_init(), which runs on every CPU, contains a lot of code which
    should be init-only, and is the only reason why opt_ler can't be in 
initdata.
    
    Write a brand new init_ler() which expects all future Intel and AMD CPUs to
    continue using the architectural MSRs, and does all setup together.  Call it
    from trap_init(), and remove the setup logic percpu_traps_init() except for
    the single path configuring MSR_IA32_DEBUGCTLMSR.
    
    Leave behind a warning if the user asked for LER and Xen couldn't enable it.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/traps.c | 86 ++++++++++++++++++++++++----------------------------
 1 file changed, 39 insertions(+), 47 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index fd8a4448e3..87b30ce4df 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -114,7 +114,7 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct tss_page, tss_page);
 static int debug_stack_lines = 20;
 integer_param("debug_stack_lines", debug_stack_lines);
 
-static bool __ro_after_init opt_ler;
+static bool __initdata opt_ler;
 boolean_param("ler", opt_ler);
 
 /* LastExceptionFromIP on this hardware.  Zero if LER is not in use. */
@@ -2092,56 +2092,10 @@ static void __init set_intr_gate(unsigned int n, void 
*addr)
     __set_intr_gate(n, 0, addr);
 }
 
-static unsigned int noinline __init calc_ler_msr(void)
-{
-    switch ( boot_cpu_data.x86_vendor )
-    {
-    case X86_VENDOR_INTEL:
-        switch ( boot_cpu_data.x86 )
-        {
-        case 6:
-            return MSR_IA32_LASTINTFROMIP;
-
-        case 15:
-            return MSR_P4_LER_FROM_LIP;
-        }
-        break;
-
-    case X86_VENDOR_AMD:
-        switch ( boot_cpu_data.x86 )
-        {
-        case 6:
-        case 0xf ... 0x19:
-            return MSR_IA32_LASTINTFROMIP;
-        }
-        break;
-
-    case X86_VENDOR_HYGON:
-        return MSR_IA32_LASTINTFROMIP;
-    }
-
-    return 0;
-}
-
 void percpu_traps_init(void)
 {
     subarch_percpu_traps_init();
 
-    if ( !opt_ler )
-        return;
-
-    if ( !ler_msr )
-    {
-        ler_msr = calc_ler_msr();
-        if ( !ler_msr )
-        {
-            opt_ler = false;
-            return;
-        }
-
-        setup_force_cpu_cap(X86_FEATURE_XEN_LBR);
-    }
-
     if ( cpu_has_xen_lbr )
         wrmsrl(MSR_IA32_DEBUGCTLMSR, IA32_DEBUGCTLMSR_LBR);
 }
@@ -2201,6 +2155,42 @@ void __init init_idt_traps(void)
         this_cpu(compat_gdt) = boot_compat_gdt;
 }
 
+static void __init init_ler(void)
+{
+    unsigned int msr = 0;
+
+    if ( !opt_ler )
+        return;
+
+    /*
+     * Intel Pentium 4 is the only known CPU to not use the architectural MSR
+     * indicies.
+     */
+    switch ( boot_cpu_data.x86_vendor )
+    {
+    case X86_VENDOR_INTEL:
+        if ( boot_cpu_data.x86 == 0xf )
+        {
+            msr = MSR_P4_LER_FROM_LIP;
+            break;
+        }
+        fallthrough;
+    case X86_VENDOR_AMD:
+    case X86_VENDOR_HYGON:
+        msr = MSR_IA32_LASTINTFROMIP;
+        break;
+    }
+
+    if ( msr == 0 )
+    {
+        printk(XENLOG_WARNING "LER disabled: failed to identify MSRs\n");
+        return;
+    }
+
+    ler_msr = msr;
+    setup_force_cpu_cap(X86_FEATURE_XEN_LBR);
+}
+
 extern void (*const autogen_entrypoints[X86_NR_VECTORS])(void);
 void __init trap_init(void)
 {
@@ -2226,6 +2216,8 @@ void __init trap_init(void)
         }
     }
 
+    init_ler();
+
     /* Cache {,compat_}gdt_l1e now that physically relocation is done. */
     this_cpu(gdt_l1e) =
         l1e_from_pfn(virt_to_mfn(boot_gdt), __PAGE_HYPERVISOR_RW);
--
generated by git-patchbot for /home/xen/git/xen.git#staging