[PATCH for-4.14] x86/ucode: Fix errors with start/end_update()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s 9267a439c "x86/ucode: Document the behaviour of the microcode_ops hooks"
identified several poor behaviours of the start_update()/end_update_percpu()
hooks.

AMD have subsequently confirmed that OSVW don't, and are not expected to,
change across a microcode load, rendering all of this complexity unecessary.

Instead of fixing up the logic to not leave the OSVW state reset in a number
of corner cases, delete the logic entirely.  This in turn allows for the
removal of the poorly-named 'start_update' parameter to
microcode_update_one().

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Paul Durrant <paul@xxxxxxx>

This wants backporting to 4.13, hence considering for 4.14 at this point.
---
 xen/arch/x86/acpi/power.c            |  2 +-
 xen/arch/x86/cpu/microcode/amd.c     | 17 -----------------
 xen/arch/x86/cpu/microcode/core.c    | 33 +++------------------------------
 xen/arch/x86/cpu/microcode/private.h | 14 --------------
 xen/arch/x86/smpboot.c               |  2 +-
 xen/include/asm-x86/microcode.h      |  2 +-
 6 files changed, 6 insertions(+), 64 deletions(-)

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index 0cda362045..dfffe08e18 100644
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -287,7 +287,7 @@ static int enter_state(u32 state)
     console_end_sync();
     watchdog_enable();
 
-    microcode_update_one(true);
+    microcode_update_one();
 
     if ( !recheck_cpu_features(0) )
         panic("Missing previously available feature(s)\n");
diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 3f0969e70d..11e24637e7 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -395,26 +395,9 @@ static struct microcode_patch *cpu_request_microcode(const 
void *buf, size_t siz
     return patch;
 }
 
-#ifdef CONFIG_HVM
-static int start_update(void)
-{
-    /*
-     * svm_host_osvw_init() will be called on each cpu by calling '.end_update'
-     * in common code.
-     */
-    svm_host_osvw_reset();
-
-    return 0;
-}
-#endif
-
 const struct microcode_ops amd_ucode_ops = {
     .cpu_request_microcode            = cpu_request_microcode,
     .collect_cpu_info                 = collect_cpu_info,
     .apply_microcode                  = apply_microcode,
-#ifdef CONFIG_HVM
-    .start_update                     = start_update,
-    .end_update_percpu                = svm_host_osvw_init,
-#endif
     .compare_patch                    = compare_patch,
 };
diff --git a/xen/arch/x86/cpu/microcode/core.c 
b/xen/arch/x86/cpu/microcode/core.c
index d879d28787..18ebc07b13 100644
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -546,9 +546,6 @@ static int do_microcode_update(void *patch)
     else
         ret = secondary_thread_fn();
 
-    if ( microcode_ops->end_update_percpu )
-        microcode_ops->end_update_percpu();
-
     return ret;
 }
 
@@ -620,16 +617,6 @@ static long microcode_update_helper(void *data)
     }
     spin_unlock(&microcode_mutex);
 
-    if ( microcode_ops->start_update )
-    {
-        ret = microcode_ops->start_update();
-        if ( ret )
-        {
-            microcode_free_patch(patch);
-            goto put;
-        }
-    }
-
     cpumask_clear(&cpu_callin_map);
     atomic_set(&cpu_out, 0);
     atomic_set(&cpu_updated, 0);
@@ -728,28 +715,14 @@ static int __init microcode_init(void)
 __initcall(microcode_init);
 
 /* Load a cached update to current cpu */
-int microcode_update_one(bool start_update)
+int microcode_update_one(void)
 {
-    int err;
-
     if ( !microcode_ops )
         return -EOPNOTSUPP;
 
     microcode_ops->collect_cpu_info();
 
-    if ( start_update && microcode_ops->start_update )
-    {
-        err = microcode_ops->start_update();
-        if ( err )
-            return err;
-    }
-
-    err = microcode_update_cpu(NULL);
-
-    if ( microcode_ops->end_update_percpu )
-        microcode_ops->end_update_percpu();
-
-    return err;
+    return microcode_update_cpu(NULL);
 }
 
 /* BSP calls this function to parse ucode blob and then apply an update. */
@@ -790,7 +763,7 @@ static int __init early_microcode_update_cpu(void)
     spin_unlock(&microcode_mutex);
     ASSERT(rc);
 
-    return microcode_update_one(true);
+    return microcode_update_one();
 }
 
 int __init early_microcode_init(void)
diff --git a/xen/arch/x86/cpu/microcode/private.h 
b/xen/arch/x86/cpu/microcode/private.h
index dc5c7a81ae..c00ba590d1 100644
--- a/xen/arch/x86/cpu/microcode/private.h
+++ b/xen/arch/x86/cpu/microcode/private.h
@@ -46,20 +46,6 @@ struct microcode_ops {
     int (*apply_microcode)(const struct microcode_patch *patch);
 
     /*
-     * Optional.  If provided and applicable to the specific update attempt,
-     * is run once by the initiating CPU.  Returning an error will abort the
-     * load attempt.
-     */
-    int (*start_update)(void);
-
-    /*
-     * Optional.  If provided, called on every CPU which completes a microcode
-     * load.  May be called in the case of some errors, and not others.  May
-     * be called even if start_update() wasn't.
-     */
-    void (*end_update_percpu)(void);
-
-    /*
      * Given two patches, are they both applicable to the current CPU, and is
      * new a higher revision than old?
      */
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 13b3dade9c..f878a00760 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -369,7 +369,7 @@ void start_secondary(void *unused)
 
     initialize_cpu_data(cpu);
 
-    microcode_update_one(false);
+    microcode_update_one();
 
     /*
      * If MSR_SPEC_CTRL is available, apply Xen's default setting and discard
diff --git a/xen/include/asm-x86/microcode.h b/xen/include/asm-x86/microcode.h
index 9da63f992e..3b0234e9fa 100644
--- a/xen/include/asm-x86/microcode.h
+++ b/xen/include/asm-x86/microcode.h
@@ -22,6 +22,6 @@ DECLARE_PER_CPU(struct cpu_signature, cpu_sig);
 void microcode_set_module(unsigned int idx);
 int microcode_update(XEN_GUEST_HANDLE(const_void), unsigned long len);
 int early_microcode_init(void);
-int microcode_update_one(bool start_update);
+int microcode_update_one(void);
 
 #endif /* ASM_X86__MICROCODE_H */
-- 
2.11.0