[Xen-changelog] [xen master] x86: Begin to remove TSC mode PVRDTSCP

[patchbot@xxxxxxx]

commit a4ac3d40ec4c412c337d039b7483fc39ec4871d3
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Feb 19 13:35:58 2018 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Dec 18 17:13:51 2018 +0000

    x86: Begin to remove TSC mode PVRDTSCP
    
    For more historical context, see
      c/s c17b36d5dc792cfdf59b6de0213b168bec0af8e8
      c/s 04656384a1b9714e43db850c51431008e23450d8
    
    PVRDTSCP was an attempt to provide Xen-aware userspace with a stable 
monotonic
    clock, and enough information for said userspace to cope with frequency
    changes across migrate.  However, the PVRDTSCP infrastructure has resulted 
in
    very tangled code, and non-architectural behaviour even in non-PVRDTSCP 
cases.
    
    Seeing as the functionality has been replaced entirely by improvements in PV
    clocks (including being plumbed into the VDSO nowadays), or alternatively by
    hardware TSC scaling features, and no-one is aware of any users of this 
mode,
    take the opportunity to remove it.
    
    For now, drop TSC_MODE_PVRDTSCP from tsc_{get,set}_info().  This will catch
    and cleanly reject attempts to migrate in a VM configured to use PVRDTSCP,
    rather than letting it run and have the wrong timing mode.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/time.c        | 35 -----------------------------------
 xen/include/asm-x86/time.h |  5 +----
 2 files changed, 1 insertion(+), 39 deletions(-)

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index d80a5868a0..9a6ea8ffcb 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -2165,21 +2165,6 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
         *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns);
         *gtsc_khz = enable_tsc_scaling ? d->arch.tsc_khz : cpu_khz;
         break;
-    case TSC_MODE_PVRDTSCP:
-        if ( d->arch.vtsc )
-        {
-            *elapsed_nsec = get_s_time() - d->arch.vtsc_offset;
-            *gtsc_khz = cpu_khz;
-        }
-        else
-        {
-            tsc = rdtsc();
-            *elapsed_nsec = scale_delta(tsc, &this_cpu(cpu_time).tsc_scale) -
-                            d->arch.vtsc_offset;
-            *gtsc_khz = enable_tsc_scaling ? d->arch.tsc_khz
-                                           : 0 /* ignored by tsc_set_info */;
-        }
-        break;
     }
 
     if ( (int64_t)*elapsed_nsec < 0 )
@@ -2208,8 +2193,6 @@ int tsc_set_info(struct domain *d,
 
     switch ( tsc_mode )
     {
-        bool enable_tsc_scaling;
-
     case TSC_MODE_DEFAULT:
     case TSC_MODE_ALWAYS_EMULATE:
         d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
@@ -2235,24 +2218,6 @@ int tsc_set_info(struct domain *d,
         d->arch.vtsc = 1;
         d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
         break;
-    case TSC_MODE_PVRDTSCP:
-        d->arch.vtsc = !boot_cpu_has(X86_FEATURE_RDTSCP) ||
-                       !host_tsc_is_safe();
-        enable_tsc_scaling = is_hvm_domain(d) && !d->arch.vtsc &&
-                             hvm_get_tsc_scaling_ratio(gtsc_khz ?: cpu_khz);
-        d->arch.tsc_khz = (enable_tsc_scaling && gtsc_khz) ? gtsc_khz : 
cpu_khz;
-        set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
-        d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
-        if ( d->arch.vtsc )
-            d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
-        else {
-            /* when using native TSC, offset is nsec relative to power-on
-             * of physical machine */
-            d->arch.vtsc_offset = scale_delta(rdtsc(),
-                                              &this_cpu(cpu_time).tsc_scale) -
-                                  elapsed_nsec;
-        }
-        break;
 
     default:
         return -EINVAL;
diff --git a/xen/include/asm-x86/time.h b/xen/include/asm-x86/time.h
index b85688dcfb..4f3d926884 100644
--- a/xen/include/asm-x86/time.h
+++ b/xen/include/asm-x86/time.h
@@ -12,10 +12,7 @@
  *    2 = guest rdtsc always executed natively (no monotonicity/frequency
  *         guarantees); guest rdtscp emulated at native frequency if
  *         unsupported by h/w, else executed natively
- *    3 = same as 2, except xen manages TSC_AUX register so guest can
- *         determine when a restore/migration has occurred and assumes
- *         guest obtains/uses pvclock-like mechanism to adjust for
- *         monotonicity and frequency changes
+ *    3 = Removed, was PVRDTSCP.
  */
 #define TSC_MODE_DEFAULT          0
 #define TSC_MODE_ALWAYS_EMULATE   1
--
generated by git-patchbot for /home/xen/git/xen.git#master

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