[Xen-devel] [PATCH v2 2/5] x86: Begin to remove TSC mode PVRDTSCP

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

v2:
 * Split tsc_set_info() changes out into an earlier patch.  Reword commit
   message appropriately.
---
 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 d80a586..9a6ea8f 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 6111fdc..6398264 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
-- 
2.1.4


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