[PATCH v2 0/5] x86: Drop PVRDTSCP and fix MSR_TSC_AUX handling for guests

[PATCH v2 0/5] x86: Drop PVRDTSCP and fix MSR_TSC_AUX handling for guests

[Andrew Cooper]

Boris has confirmed that noone appears to be using PVRDTSCP any more, and in
the decade since it was introduced, guest kernel / hardware support has
provided a better alternative.

For changes, see individual patches.

Andrew Cooper (5):
  x86/time: Alter tsc_set_info() to return an error value
  x86: Begin to remove TSC mode PVRDTSCP
  x86/pv: Remove deferred RDTSC{,P} handling in pv_emulate_privileged_op()
  x86/msr: Handle MSR_TSC_AUX consistently for PV and HVM guests
  x86/pv: Expose RDTSCP to PV guests

 xen/arch/x86/domain.c                       |  9 +++--
 xen/arch/x86/domctl.c                       | 10 +++---
 xen/arch/x86/hvm/hvm.c                      | 22 +++++-------
 xen/arch/x86/hvm/svm/svm.c                  |  6 ++--
 xen/arch/x86/hvm/vmx/vmx.c                  |  6 ++--
 xen/arch/x86/msr.c                          | 18 ++++++++++
 xen/arch/x86/pv/emul-inv-op.c               | 27 +--------------
 xen/arch/x86/pv/emul-priv-op.c              | 32 +----------------
 xen/arch/x86/time.c                         | 53 +++++++----------------------
 xen/include/asm-x86/cpufeature.h            |  5 +++
 xen/include/asm-x86/hvm/hvm.h               |  6 ----
 xen/include/asm-x86/hvm/vcpu.h              |  1 -
 xen/include/asm-x86/msr.h                   |  9 +++++
 xen/include/asm-x86/time.h                  | 13 +++----
 xen/include/public/arch-x86/cpufeatureset.h |  2 +-
 15 files changed, 77 insertions(+), 142 deletions(-)

-- 
2.1.4


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[PATCH v2 1/5] x86/time: Alter tsc_set_info() to return an error value

[Andrew Cooper]

Currently, tsc_set_info() performs no parameter checking, and an invalid
tsc_mode goes largely unnoticed.  Fix it to reject invalid tsc_modes with
-EINVAL, and update the callers to check the return value.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Roger Pau Monné <roger.pau@citrix.com>

v2:
 * New
---
 xen/arch/x86/domain.c      |  4 ++--
 xen/arch/x86/domctl.c      |  8 ++++----
 xen/arch/x86/time.c        | 18 +++++++++++++-----
 xen/include/asm-x86/time.h |  7 +++----
 4 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 295b10c..245300b 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -599,8 +599,8 @@ int arch_domain_create(struct domain *d,
     else
         ASSERT_UNREACHABLE(); /* Not HVM and not PV? */
 
-    /* initialize default tsc behavior in case tools don't */
-    tsc_set_info(d, TSC_MODE_DEFAULT, 0UL, 0, 0);
+    if ( (rc = tsc_set_info(d, TSC_MODE_DEFAULT, 0UL, 0, 0)) != 0 )
+        goto fail;
 
     /* PV/PVH guests get an emulated PIT too for video BIOSes to use. */
     pit_init(d, cpu_khz);
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index aa8ad19..ed46df8 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -975,10 +975,10 @@ long arch_do_domctl(
         else
         {
             domain_pause(d);
-            tsc_set_info(d, domctl->u.tsc_info.tsc_mode,
-                         domctl->u.tsc_info.elapsed_nsec,
-                         domctl->u.tsc_info.gtsc_khz,
-                         domctl->u.tsc_info.incarnation);
+            ret = tsc_set_info(d, domctl->u.tsc_info.tsc_mode,
+                               domctl->u.tsc_info.elapsed_nsec,
+                               domctl->u.tsc_info.gtsc_khz,
+                               domctl->u.tsc_info.incarnation);
             domain_unpause(d);
         }
         break;
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 24d4c27..d80a586 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -2194,19 +2194,19 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
  * only the last "sticks" and all are completed before the guest executes
  * an rdtsc instruction
  */
-void tsc_set_info(struct domain *d,
-                  uint32_t tsc_mode, uint64_t elapsed_nsec,
-                  uint32_t gtsc_khz, uint32_t incarnation)
+int tsc_set_info(struct domain *d,
+                 uint32_t tsc_mode, uint64_t elapsed_nsec,
+                 uint32_t gtsc_khz, uint32_t incarnation)
 {
     ASSERT(!is_system_domain(d));
 
     if ( is_pv_domain(d) && is_hardware_domain(d) )
     {
         d->arch.vtsc = 0;
-        return;
+        return 0;
     }
 
-    switch ( d->arch.tsc_mode = tsc_mode )
+    switch ( tsc_mode )
     {
         bool enable_tsc_scaling;
 
@@ -2253,7 +2253,13 @@ void tsc_set_info(struct domain *d,
                                   elapsed_nsec;
         }
         break;
+
+    default:
+        return -EINVAL;
     }
+
+    d->arch.tsc_mode = tsc_mode;
+
     d->arch.incarnation = incarnation + 1;
     if ( is_hvm_domain(d) )
     {
@@ -2280,6 +2286,8 @@ void tsc_set_info(struct domain *d,
     }
 
     recalculate_cpuid_policy(d);
+
+    return 0;
 }
 
 /* vtsc may incur measurable performance degradation, diagnose with this */
diff --git a/xen/include/asm-x86/time.h b/xen/include/asm-x86/time.h
index ce96ec9..6111fdc 100644
--- a/xen/include/asm-x86/time.h
+++ b/xen/include/asm-x86/time.h
@@ -60,12 +60,11 @@ uint64_t pv_soft_rdtsc(const struct vcpu *v, const struct cpu_user_regs *regs);
 u64 gtime_to_gtsc(struct domain *d, u64 time);
 u64 gtsc_to_gtime(struct domain *d, u64 tsc);
 
-void tsc_set_info(struct domain *d, uint32_t tsc_mode, uint64_t elapsed_nsec,
-                  uint32_t gtsc_khz, uint32_t incarnation);
-   
+int tsc_set_info(struct domain *d, uint32_t tsc_mode, uint64_t elapsed_nsec,
+                 uint32_t gtsc_khz, uint32_t incarnation);
+
 void tsc_get_info(struct domain *d, uint32_t *tsc_mode, uint64_t *elapsed_nsec,
                   uint32_t *gtsc_khz, uint32_t *incarnation);
-   
 
 void force_update_vcpu_system_time(struct vcpu *v);
 
-- 
2.1.4


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

[Andrew Cooper]

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

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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[PATCH v2 3/5] x86/pv: Remove deferred RDTSC{, P} handling in pv_emulate_privileged_op()

[Andrew Cooper]

As noted in c/s 4999bf3e8b "x86/PV: use generic emulator for privileged
instruction handling", these hoops are jumped through to retain the older
behaviour, along with a note suggesting that we should reconsider things.

Part of the reason for retention of the old behaviour was removed by c/s
5b04262079 "x86/time: Rework pv_soft_rdtsc() to aid further cleanup" which in
particular caused it to not write regs->rcx directly.

It does not matter exactly when pv_soft_rdtsc() is called, as Xen's behaviour
is an opaque atomic action from the guests point of view.

Drop all the deferral logic, and leave TSC_AUX uniformly at 0 as PVRDTSCP mode
is being removed.  Later changes will make this behave architecturally.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
CC: Wei Liu <wei.liu2@citrix.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>

v2:
 * Extend the commit message.
---
 xen/arch/x86/pv/emul-priv-op.c | 30 ++----------------------------
 1 file changed, 2 insertions(+), 28 deletions(-)

diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index a84f3f1..5133c35 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -51,9 +51,6 @@ struct priv_op_ctxt {
     } cs;
     char *io_emul_stub;
     unsigned int bpmatch;
-    unsigned int tsc;
-#define TSC_BASE 1
-#define TSC_AUX 2
 };
 
 /* I/O emulation support. Helper routines for, and type of, the stack stub. */
@@ -810,7 +807,6 @@ static inline bool is_cpufreq_controller(const struct domain *d)
 static int read_msr(unsigned int reg, uint64_t *val,
                     struct x86_emulate_ctxt *ctxt)
 {
-    struct priv_op_ctxt *poc = container_of(ctxt, struct priv_op_ctxt, ctxt);
     const struct vcpu *curr = current;
     const struct domain *currd = curr->domain;
     bool vpmu_msr = false;
@@ -847,19 +843,11 @@ static int read_msr(unsigned int reg, uint64_t *val,
         *val = curr->arch.pv.gs_base_user;
         return X86EMUL_OKAY;
 
-    /*
-     * In order to fully retain original behavior, defer calling
-     * pv_soft_rdtsc() until after emulation. This may want/need to be
-     * reconsidered.
-     */
     case MSR_IA32_TSC:
-        poc->tsc |= TSC_BASE;
-        goto normal;
+        *val = currd->arch.vtsc ? pv_soft_rdtsc(curr, ctxt->regs) : rdtsc();
+        return X86EMUL_OKAY;
 
     case MSR_TSC_AUX:
-        poc->tsc |= TSC_AUX;
-        if ( cpu_has_rdtscp )
-            goto normal;
         *val = 0;
         return X86EMUL_OKAY;
 
@@ -1313,20 +1301,6 @@ int pv_emulate_privileged_op(struct cpu_user_regs *regs)
     switch ( rc )
     {
     case X86EMUL_OKAY:
-        if ( ctxt.tsc & TSC_BASE )
-        {
-            if ( currd->arch.vtsc || (ctxt.tsc & TSC_AUX) )
-            {
-                msr_split(regs, pv_soft_rdtsc(curr, regs));
-
-                if ( ctxt.tsc & TSC_AUX )
-                    regs->rcx = (currd->arch.tsc_mode == TSC_MODE_PVRDTSCP
-                                 ? currd->arch.incarnation : 0);
-            }
-            else
-                msr_split(regs, rdtsc());
-        }
-
         if ( ctxt.ctxt.retire.singlestep )
             ctxt.bpmatch |= DR_STEP;
         if ( ctxt.bpmatch )
-- 
2.1.4


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[PATCH v2 4/5] x86/msr: Handle MSR_TSC_AUX consistently for PV and HVM guests

[Andrew Cooper]

With PVRDTSCP mode removed, handling of MSR_TSC_AUX can move into the common
code.  Move its storage into struct vcpu_msrs (dropping the HVM-specific
msr_tsc_aux), and add an RDPID feature check as this bit also enumerates the
presence of the MSR.

Introduce cpu_has_rdpid along with the synthesized cpu_has_msr_tsc_aux to
correct the context switch paths, as MSR_TSC_AUX is enumerated by either
RDTSCP or RDPID.

Drop hvm_msr_tsc_aux() entirely, and use v->arch.msrs->tsc_aux directly.
Update hvm_load_cpu_ctxt() to check that the incoming ctxt.msr_tsc_aux isn't
out of range.  In practice, no previous version of Xen ever wrote an
out-of-range value.  Add MSR_TSC_AUX to the list of MSRs migrated for PV
guests, but leave the HVM path using the existing space in hvm_hw_cpu.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Jun Nakajima <jun.nakajima@intel.com>
CC: Kevin Tian <kevin.tian@intel.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
CC: Brian Woods <brian.woods@amd.com>

v2:
 * Rebase over "x86/msr: Handle MSR_AMD64_DR{0-3}_ADDRESS_MASK in the new MSR infrastructure"
 * Move the HVM msr_tsc_aux check earlier in hvm_load_cpu_ctxt()
 * Introduce cpu_has_msr_tsc_aux

RFC: I'm not overly happy with cpu_has_msr_tsc_aux because in practice all
hardware with rdpid has rdtscp, making this an effectively dead conditional in
the context switch path.  I'm tempted to go with

  #define cpu_has_msr_tsc_aux     (cpu_has_rdtscp /* || cpu_has_rdpid */)

to get the point across, but without the extra jump.
---
 xen/arch/x86/domain.c            |  5 ++---
 xen/arch/x86/domctl.c            |  2 ++
 xen/arch/x86/hvm/hvm.c           | 22 +++++++++-------------
 xen/arch/x86/hvm/svm/svm.c       |  6 +++---
 xen/arch/x86/hvm/vmx/vmx.c       |  6 +++---
 xen/arch/x86/msr.c               | 18 ++++++++++++++++++
 xen/arch/x86/pv/emul-priv-op.c   |  4 ----
 xen/include/asm-x86/cpufeature.h |  5 +++++
 xen/include/asm-x86/hvm/hvm.h    |  6 ------
 xen/include/asm-x86/hvm/vcpu.h   |  1 -
 xen/include/asm-x86/msr.h        |  9 +++++++++
 11 files changed, 51 insertions(+), 33 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 245300b..38c233e 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1592,9 +1592,8 @@ void paravirt_ctxt_switch_to(struct vcpu *v)
     if ( unlikely(v->arch.dr7 & DR7_ACTIVE_MASK) )
         activate_debugregs(v);
 
-    if ( cpu_has_rdtscp )
-        wrmsr_tsc_aux(v->domain->arch.tsc_mode == TSC_MODE_PVRDTSCP
-                      ? v->domain->arch.incarnation : 0);
+    if ( cpu_has_msr_tsc_aux )
+        wrmsr_tsc_aux(v->arch.msrs->tsc_aux);
 }
 
 /* Update per-VCPU guest runstate shared memory area (if registered). */
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index ed46df8..9bf2d08 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -1274,6 +1274,7 @@ long arch_do_domctl(
         static const uint32_t msrs_to_send[] = {
             MSR_SPEC_CTRL,
             MSR_INTEL_MISC_FEATURES_ENABLES,
+            MSR_TSC_AUX,
             MSR_AMD64_DR0_ADDRESS_MASK,
             MSR_AMD64_DR1_ADDRESS_MASK,
             MSR_AMD64_DR2_ADDRESS_MASK,
@@ -1373,6 +1374,7 @@ long arch_do_domctl(
                 {
                 case MSR_SPEC_CTRL:
                 case MSR_INTEL_MISC_FEATURES_ENABLES:
+                case MSR_TSC_AUX:
                 case MSR_AMD64_DR0_ADDRESS_MASK:
                 case MSR_AMD64_DR1_ADDRESS_MASK ... MSR_AMD64_DR3_ADDRESS_MASK:
                     if ( guest_wrmsr(v, msr.index, msr.value) != X86EMUL_OKAY )
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index e2e4204..1f9bafc 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -774,7 +774,7 @@ static int hvm_save_cpu_ctxt(struct vcpu *v, hvm_domain_context_t *h)
     struct segment_register seg;
     struct hvm_hw_cpu ctxt = {
         .tsc = hvm_get_guest_tsc_fixed(v, v->domain->arch.hvm.sync_tsc),
-        .msr_tsc_aux = hvm_msr_tsc_aux(v),
+        .msr_tsc_aux = v->arch.msrs->tsc_aux,
         .rax = v->arch.user_regs.rax,
         .rbx = v->arch.user_regs.rbx,
         .rcx = v->arch.user_regs.rcx,
@@ -1014,6 +1014,13 @@ static int hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
         return -EINVAL;
     }
 
+    if ( ctxt.msr_tsc_aux != (uint32_t)ctxt.msr_tsc_aux )
+    {
+        printk(XENLOG_G_ERR "%pv: HVM restore: bad MSR_TSC_AUX %#"PRIx64"\n",
+               v, ctxt.msr_tsc_aux);
+        return -EINVAL;
+    }
+
     /* Older Xen versions used to save the segment arbytes directly 
      * from the VMCS on Intel hosts.  Detect this and rearrange them
      * into the struct segment_register format. */
@@ -1040,7 +1047,7 @@ static int hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
     if ( hvm_funcs.tsc_scaling.setup )
         hvm_funcs.tsc_scaling.setup(v);
 
-    v->arch.hvm.msr_tsc_aux = ctxt.msr_tsc_aux;
+    v->arch.msrs->tsc_aux = ctxt.msr_tsc_aux;
 
     hvm_set_guest_tsc_fixed(v, ctxt.tsc, d->arch.hvm.sync_tsc);
 
@@ -3406,10 +3413,6 @@ int hvm_msr_read_intercept(unsigned int msr, uint64_t *msr_content)
         *msr_content = v->arch.hvm.msr_tsc_adjust;
         break;
 
-    case MSR_TSC_AUX:
-        *msr_content = hvm_msr_tsc_aux(v);
-        break;
-
     case MSR_IA32_APICBASE:
         *msr_content = vcpu_vlapic(v)->hw.apic_base_msr;
         break;
@@ -3562,13 +3565,6 @@ int hvm_msr_write_intercept(unsigned int msr, uint64_t msr_content,
         hvm_set_guest_tsc_adjust(v, msr_content);
         break;
 
-    case MSR_TSC_AUX:
-        v->arch.hvm.msr_tsc_aux = (uint32_t)msr_content;
-        if ( cpu_has_rdtscp
-             && (v->domain->arch.tsc_mode != TSC_MODE_PVRDTSCP) )
-            wrmsr_tsc_aux(msr_content);
-        break;
-
     case MSR_IA32_APICBASE:
         if ( !vlapic_msr_set(vcpu_vlapic(v), msr_content) )
             goto gp_fault;
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index b9a8900..df6f262 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1069,8 +1069,8 @@ static void svm_ctxt_switch_to(struct vcpu *v)
     svm_lwp_load(v);
     svm_tsc_ratio_load(v);
 
-    if ( cpu_has_rdtscp )
-        wrmsr_tsc_aux(hvm_msr_tsc_aux(v));
+    if ( cpu_has_msr_tsc_aux )
+        wrmsr_tsc_aux(v->arch.msrs->tsc_aux);
 }
 
 static void noreturn svm_do_resume(struct vcpu *v)
@@ -2968,7 +2968,7 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
         break;
 
     case VMEXIT_RDTSCP:
-        regs->rcx = hvm_msr_tsc_aux(v);
+        regs->rcx = v->arch.msrs->tsc_aux;
         /* fall through */
     case VMEXIT_RDTSC:
         svm_vmexit_do_rdtsc(regs);
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 365eeb2..9b691d9 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -511,8 +511,8 @@ static void vmx_restore_guest_msrs(struct vcpu *v)
     wrmsrl(MSR_LSTAR,          v->arch.hvm.vmx.lstar);
     wrmsrl(MSR_SYSCALL_MASK,   v->arch.hvm.vmx.sfmask);
 
-    if ( cpu_has_rdtscp )
-        wrmsr_tsc_aux(hvm_msr_tsc_aux(v));
+    if ( cpu_has_msr_tsc_aux )
+        wrmsr_tsc_aux(v->arch.msrs->tsc_aux);
 }
 
 void vmx_update_cpu_exec_control(struct vcpu *v)
@@ -3956,7 +3956,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
         vmx_invlpg_intercept(exit_qualification);
         break;
     case EXIT_REASON_RDTSCP:
-        regs->rcx = hvm_msr_tsc_aux(v);
+        regs->rcx = v->arch.msrs->tsc_aux;
         /* fall through */
     case EXIT_REASON_RDTSC:
         update_guest_eip(); /* Safe: RDTSC, RDTSCP */
diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index 76cb6ef..f86da8f 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -162,6 +162,13 @@ int guest_rdmsr(const struct vcpu *v, uint32_t msr, uint64_t *val)
         ret = guest_rdmsr_xen(v, msr, val);
         break;
 
+    case MSR_TSC_AUX:
+        if ( !cp->extd.rdtscp && !cp->feat.rdpid )
+            goto gp_fault;
+
+        *val = msrs->tsc_aux;
+        break;
+
     case MSR_AMD64_DR0_ADDRESS_MASK:
     case MSR_AMD64_DR1_ADDRESS_MASK ... MSR_AMD64_DR3_ADDRESS_MASK:
         if ( !cp->extd.dbext )
@@ -309,6 +316,17 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
         ret = guest_wrmsr_xen(v, msr, val);
         break;
 
+    case MSR_TSC_AUX:
+        if ( !cp->extd.rdtscp && !cp->feat.rdpid )
+            goto gp_fault;
+        if ( val != (uint32_t)val )
+            goto gp_fault;
+
+        msrs->tsc_aux = val;
+        if ( v == curr )
+            wrmsr_tsc_aux(val);
+        break;
+
     case MSR_AMD64_DR0_ADDRESS_MASK:
     case MSR_AMD64_DR1_ADDRESS_MASK ... MSR_AMD64_DR3_ADDRESS_MASK:
         if ( !cp->extd.dbext || val != (uint32_t)val )
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 5133c35..942ece2 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -847,10 +847,6 @@ static int read_msr(unsigned int reg, uint64_t *val,
         *val = currd->arch.vtsc ? pv_soft_rdtsc(curr, ctxt->regs) : rdtsc();
         return X86EMUL_OKAY;
 
-    case MSR_TSC_AUX:
-        *val = 0;
-        return X86EMUL_OKAY;
-
     case MSR_EFER:
         /* Hide unknown bits, and unconditionally hide SVME from guests. */
         *val = read_efer() & EFER_KNOWN_MASK & ~EFER_SVME;
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index c2b0f6a..5592e17 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -107,6 +107,9 @@
 #define cpu_has_avx512bw        boot_cpu_has(X86_FEATURE_AVX512BW)
 #define cpu_has_avx512vl        boot_cpu_has(X86_FEATURE_AVX512VL)
 
+/* CPUID level 0x00000007:0.ecx */
+#define cpu_has_rdpid           boot_cpu_has(X86_FEATURE_RDPID)
+
 /* CPUID level 0x80000007.edx */
 #define cpu_has_itsc            boot_cpu_has(X86_FEATURE_ITSC)
 
@@ -117,6 +120,8 @@
 #define cpu_has_lfence_dispatch boot_cpu_has(X86_FEATURE_LFENCE_DISPATCH)
 #define cpu_has_xen_lbr         boot_cpu_has(X86_FEATURE_XEN_LBR)
 
+#define cpu_has_msr_tsc_aux     (cpu_has_rdtscp || cpu_has_rdpid)
+
 enum _cache_type {
     CACHE_TYPE_NULL = 0,
     CACHE_TYPE_DATA = 1,
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 3d3250d..3a92bb3 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -563,12 +563,6 @@ static inline void hvm_invalidate_regs_fields(struct cpu_user_regs *regs)
 #endif
 }
 
-#define hvm_msr_tsc_aux(v) ({                                               \
-    struct domain *__d = (v)->domain;                                       \
-    (__d->arch.tsc_mode == TSC_MODE_PVRDTSCP)                               \
-        ? (u32)__d->arch.incarnation : (u32)(v)->arch.hvm.msr_tsc_aux;      \
-})
-
 /*
  * Nested HVM
  */
diff --git a/xen/include/asm-x86/hvm/vcpu.h b/xen/include/asm-x86/hvm/vcpu.h
index 39778f9..c8a40f6 100644
--- a/xen/include/asm-x86/hvm/vcpu.h
+++ b/xen/include/asm-x86/hvm/vcpu.h
@@ -170,7 +170,6 @@ struct hvm_vcpu {
 
     struct hvm_vcpu_asid n1asid;
 
-    u32                 msr_tsc_aux;
     u64                 msr_tsc_adjust;
     u64                 msr_xss;
 
diff --git a/xen/include/asm-x86/msr.h b/xen/include/asm-x86/msr.h
index 05d905b..adfa2fa 100644
--- a/xen/include/asm-x86/msr.h
+++ b/xen/include/asm-x86/msr.h
@@ -289,6 +289,15 @@ struct vcpu_msrs
     } misc_features_enables;
 
     /*
+     * 0xc0000103 - MSR_TSC_AUX
+     *
+     * Value is guest chosen, and always loaded in vcpu context.  Guests have
+     * no direct MSR access, and the value is accessible to userspace with the
+     * RDTSCP and RDPID instructions.
+     */
+    uint32_t tsc_aux;
+
+    /*
      * 0xc00110{27,19-1b} MSR_AMD64_DR{0-3}_ADDRESS_MASK
      *
      * Loaded into hardware for guests which have active %dr7 settings.
-- 
2.1.4


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[PATCH v2 5/5] x86/pv: Expose RDTSCP to PV guests

[Andrew Cooper]

The final remnanat of PVRDTSCP is that we would emulate RDTSCP even on
hardware which lacked the instruction.  RDTSCP is available on almost all
64-bit x86 hardware.

Remove this emulation, drop the TSC_MODE_PVRDTSCP constant, and allow RDTSCP
in a PV guest's CPUID policy.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 xen/arch/x86/pv/emul-inv-op.c               | 27 +--------------------------
 xen/include/asm-x86/time.h                  |  1 -
 xen/include/public/arch-x86/cpufeatureset.h |  2 +-
 3 files changed, 2 insertions(+), 28 deletions(-)

diff --git a/xen/arch/x86/pv/emul-inv-op.c b/xen/arch/x86/pv/emul-inv-op.c
index 56f5a45..91d0579 100644
--- a/xen/arch/x86/pv/emul-inv-op.c
+++ b/xen/arch/x86/pv/emul-inv-op.c
@@ -41,31 +41,6 @@
 
 #include "emulate.h"
 
-static int emulate_invalid_rdtscp(struct cpu_user_regs *regs)
-{
-    char opcode[3];
-    unsigned long eip, rc;
-    struct vcpu *v = current;
-    const struct domain *currd = v->domain;
-
-    eip = regs->rip;
-    if ( (rc = copy_from_user(opcode, (char *)eip, sizeof(opcode))) != 0 )
-    {
-        pv_inject_page_fault(0, eip + sizeof(opcode) - rc);
-        return EXCRET_fault_fixed;
-    }
-    if ( memcmp(opcode, "\xf\x1\xf9", sizeof(opcode)) )
-        return 0;
-    eip += sizeof(opcode);
-
-    msr_split(regs, pv_soft_rdtsc(v, regs));
-    regs->rcx = (currd->arch.tsc_mode == TSC_MODE_PVRDTSCP
-                 ? currd->arch.incarnation : 0);
-
-    pv_emul_instruction_done(regs, eip);
-    return EXCRET_fault_fixed;
-}
-
 static int emulate_forced_invalid_op(struct cpu_user_regs *regs)
 {
     char sig[5], instr[2];
@@ -121,7 +96,7 @@ static int emulate_forced_invalid_op(struct cpu_user_regs *regs)
 
 bool pv_emulate_invalid_op(struct cpu_user_regs *regs)
 {
-    return !emulate_invalid_rdtscp(regs) && !emulate_forced_invalid_op(regs);
+    return !emulate_forced_invalid_op(regs);
 }
 
 /*
diff --git a/xen/include/asm-x86/time.h b/xen/include/asm-x86/time.h
index 6398264..5264a86 100644
--- a/xen/include/asm-x86/time.h
+++ b/xen/include/asm-x86/time.h
@@ -17,7 +17,6 @@
 #define TSC_MODE_DEFAULT          0
 #define TSC_MODE_ALWAYS_EMULATE   1
 #define TSC_MODE_NEVER_EMULATE    2
-#define TSC_MODE_PVRDTSCP         3
 
 typedef u64 cycles_t;
 
diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index 6c82816..fbc68fa 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -156,7 +156,7 @@ XEN_CPUFEATURE(NX,            2*32+20) /*A  Execute Disable */
 XEN_CPUFEATURE(MMXEXT,        2*32+22) /*A  AMD MMX extensions */
 XEN_CPUFEATURE(FFXSR,         2*32+25) /*A  FFXSR instruction optimizations */
 XEN_CPUFEATURE(PAGE1GB,       2*32+26) /*H  1Gb large page support */
-XEN_CPUFEATURE(RDTSCP,        2*32+27) /*S  RDTSCP */
+XEN_CPUFEATURE(RDTSCP,        2*32+27) /*A  RDTSCP */
 XEN_CPUFEATURE(LM,            2*32+29) /*A  Long Mode (x86-64) */
 XEN_CPUFEATURE(3DNOWEXT,      2*32+30) /*A  AMD 3DNow! extensions */
 XEN_CPUFEATURE(3DNOW,         2*32+31) /*A  3DNow! */
-- 
2.1.4


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Re: [PATCH v2 1/5] x86/time: Alter tsc_set_info() to return an error value

[Jan Beulich]

>>> On 20.11.18 at 15:36, <andrew.cooper3@citrix.com> wrote:
> Currently, tsc_set_info() performs no parameter checking, and an invalid
> tsc_mode goes largely unnoticed.  Fix it to reject invalid tsc_modes with
> -EINVAL, and update the callers to check the return value.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
with one suggestion:

> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -599,8 +599,8 @@ int arch_domain_create(struct domain *d,
>      else
>          ASSERT_UNREACHABLE(); /* Not HVM and not PV? */
>  
> -    /* initialize default tsc behavior in case tools don't */
> -    tsc_set_info(d, TSC_MODE_DEFAULT, 0UL, 0, 0);
> +    if ( (rc = tsc_set_info(d, TSC_MODE_DEFAULT, 0UL, 0, 0)) != 0 )
> +        goto fail;

I think this should gain ASSERT_UNREACHABLE(). According to
patch context the "goto fail;" might even be omitted.

Jan



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Re: [PATCH v2 2/5] x86: Begin to remove TSC mode PVRDTSCP

[Jan Beulich]

>>> On 20.11.18 at 15:36, <andrew.cooper3@citrix.com> wrote:
> 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@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>



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Re: [PATCH v2 4/5] x86/msr: Handle MSR_TSC_AUX consistently for PV and HVM guests

[Jan Beulich]

>>> On 20.11.18 at 15:37, <andrew.cooper3@citrix.com> wrote:
> With PVRDTSCP mode removed, handling of MSR_TSC_AUX can move into the common
> code.  Move its storage into struct vcpu_msrs (dropping the HVM-specific
> msr_tsc_aux), and add an RDPID feature check as this bit also enumerates the
> presence of the MSR.
> 
> Introduce cpu_has_rdpid along with the synthesized cpu_has_msr_tsc_aux to
> correct the context switch paths, as MSR_TSC_AUX is enumerated by either
> RDTSCP or RDPID.
> 
> Drop hvm_msr_tsc_aux() entirely, and use v->arch.msrs->tsc_aux directly.
> Update hvm_load_cpu_ctxt() to check that the incoming ctxt.msr_tsc_aux isn't
> out of range.  In practice, no previous version of Xen ever wrote an
> out-of-range value.  Add MSR_TSC_AUX to the list of MSRs migrated for PV
> guests, but leave the HVM path using the existing space in hvm_hw_cpu.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> CC: Jun Nakajima <jun.nakajima@intel.com>
> CC: Kevin Tian <kevin.tian@intel.com>
> CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> CC: Brian Woods <brian.woods@amd.com>
> 
> v2:
>  * Rebase over "x86/msr: Handle MSR_AMD64_DR{0-3}_ADDRESS_MASK in the new 
> MSR infrastructure"
>  * Move the HVM msr_tsc_aux check earlier in hvm_load_cpu_ctxt()
>  * Introduce cpu_has_msr_tsc_aux
> 
> RFC: I'm not overly happy with cpu_has_msr_tsc_aux because in practice all
> hardware with rdpid has rdtscp, making this an effectively dead conditional in
> the context switch path.

Except for virtualized environments, where features can artificially
be made absent. Otherwise I certainly would be fine with ...

>  I'm tempted to go with
> 
>   #define cpu_has_msr_tsc_aux     (cpu_has_rdtscp /* || cpu_has_rdpid */)
> 
> to get the point across, but without the extra jump.

... this. Hence, however,
Reviewed-by: Jan Beulich <jbeulich@suse.com>
for the patch as it is now. A reasonable compiler should be able to
convert the || into | and a single branch anyway.

Jan


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Re: [PATCH v2 5/5] x86/pv: Expose RDTSCP to PV guests

[Jan Beulich]

>>> On 20.11.18 at 15:37, <andrew.cooper3@citrix.com> wrote:
> The final remnanat of PVRDTSCP is that we would emulate RDTSCP even on
> hardware which lacked the instruction.  RDTSCP is available on almost all
> 64-bit x86 hardware.
> 
> Remove this emulation, drop the TSC_MODE_PVRDTSCP constant, and allow RDTSCP
> in a PV guest's CPUID policy.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

In the interest of not holding up things
Acked-by: Jan Beulich <jbeulich@suse.com>
but I would have appreciated if you had responded on the v1
thread, as I continue to fail to see the meaningfully larger
attack surface with the emulation left in place.

Jan



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Re: [PATCH v2 4/5] x86/msr: Handle MSR_TSC_AUX consistently for PV and HVM guests

[Jan Beulich]

>>> On 20.11.18 at 15:37, <andrew.cooper3@citrix.com> wrote:
> With PVRDTSCP mode removed, handling of MSR_TSC_AUX can move into the common
> code.  Move its storage into struct vcpu_msrs (dropping the HVM-specific
> msr_tsc_aux), and add an RDPID feature check as this bit also enumerates the
> presence of the MSR.
> 
> Introduce cpu_has_rdpid along with the synthesized cpu_has_msr_tsc_aux to
> correct the context switch paths, as MSR_TSC_AUX is enumerated by either
> RDTSCP or RDPID.
> 
> Drop hvm_msr_tsc_aux() entirely, and use v->arch.msrs->tsc_aux directly.
> Update hvm_load_cpu_ctxt() to check that the incoming ctxt.msr_tsc_aux isn't
> out of range.  In practice, no previous version of Xen ever wrote an
> out-of-range value.  Add MSR_TSC_AUX to the list of MSRs migrated for PV
> guests, but leave the HVM path using the existing space in hvm_hw_cpu.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>[...]
> ---
>  xen/arch/x86/domain.c            |  5 ++---
>  xen/arch/x86/domctl.c            |  2 ++
>  xen/arch/x86/hvm/hvm.c           | 22 +++++++++-------------
>  xen/arch/x86/hvm/svm/svm.c       |  6 +++---
>  xen/arch/x86/hvm/vmx/vmx.c       |  6 +++---
>  xen/arch/x86/msr.c               | 18 ++++++++++++++++++
>  xen/arch/x86/pv/emul-priv-op.c   |  4 ----
>  xen/include/asm-x86/cpufeature.h |  5 +++++
>  xen/include/asm-x86/hvm/hvm.h    |  6 ------
>  xen/include/asm-x86/hvm/vcpu.h   |  1 -
>  xen/include/asm-x86/msr.h        |  9 +++++++++
>  11 files changed, 51 insertions(+), 33 deletions(-)

Btw. by the end of this series wouldn't you agree docs/misc/pvrdtscp.c
should be gone? And won't docs/man/xen-tsc-mode.pod.7 need
adjustment too?

Jan



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Re: [PATCH v2 4/5] x86/msr: Handle MSR_TSC_AUX consistently for PV and HVM guests

[Tian, Kevin]

> From: Andrew Cooper [mailto:andrew.cooper3@citrix.com]
> Sent: Tuesday, November 20, 2018 10:37 PM
> 
> With PVRDTSCP mode removed, handling of MSR_TSC_AUX can move into
> the common
> code.  Move its storage into struct vcpu_msrs (dropping the HVM-specific
> msr_tsc_aux), and add an RDPID feature check as this bit also enumerates
> the
> presence of the MSR.
> 
> Introduce cpu_has_rdpid along with the synthesized cpu_has_msr_tsc_aux
> to
> correct the context switch paths, as MSR_TSC_AUX is enumerated by either
> RDTSCP or RDPID.
> 
> Drop hvm_msr_tsc_aux() entirely, and use v->arch.msrs->tsc_aux directly.
> Update hvm_load_cpu_ctxt() to check that the incoming ctxt.msr_tsc_aux
> isn't
> out of range.  In practice, no previous version of Xen ever wrote an
> out-of-range value.  Add MSR_TSC_AUX to the list of MSRs migrated for PV
> guests, but leave the HVM path using the existing space in hvm_hw_cpu.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
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[PATCH v2 6/5] tools/docs: Remove PVRDTSCP remnants

[Andrew Cooper]

PVRDTSCP is believed-unused, and its implementation has adverse consequences
on unrelated functionality in the hypervisor.  As a result, support has been
removed.

Modify libxl to provide a slightly more helpful error message if it encounters
PVRDTSCP being selected.  While adjusting TSC handling, make libxl check for
errors from the set_tsc hypercall.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
---
 docs/man/xen-tscmode.pod.7        |  94 +-----------
 docs/man/xl.cfg.pod.5.in          |   9 +-
 docs/misc/pvrdtscp.c              | 307 --------------------------------------
 tools/libxl/libxl_x86.c           |  13 +-
 tools/python/xen/lowlevel/xc/xc.c |   2 +-
 5 files changed, 19 insertions(+), 406 deletions(-)
 delete mode 100644 docs/misc/pvrdtscp.c

diff --git a/docs/man/xen-tscmode.pod.7 b/docs/man/xen-tscmode.pod.7
index 819c61d..1d81a3f 100644
--- a/docs/man/xen-tscmode.pod.7
+++ b/docs/man/xen-tscmode.pod.7
@@ -77,9 +77,7 @@ highest performance is required.
 
 =item * B<tsc_mode=3> (PVRDTSCP).
 
-High-TSC-frequency apps may be paravirtualized (modified) to
-obtain both correctness and highest performance; any unmodified
-apps must be TSC-resilient.
+This mode has been removed.
 
 =back
 
@@ -215,30 +213,6 @@ is emulated.  Note that, though emulated, the "apparent" TSC frequency
 will be the TSC frequency of the initial physical machine, even after
 migration.
 
-For environments where both TSC-safeness AND highest performance
-even across migration is a requirement, application code can be specially
-modified to use an algorithm explicitly designed into Xen for this purpose.
-This mode (tsc_mode==3) is called PVRDTSCP, because it requires
-app paravirtualization (awareness by the app that it may be running
-on top of Xen), and utilizes a variation of the rdtsc instruction
-called rdtscp that is available on most recent generation processors.
-(The rdtscp instruction differs from the rdtsc instruction in that it
-reads not only the TSC but an additional register set by system software.)
-When a pvrdtscp-modified app is running on a processor that is both TSC-safe
-and supports the rdtscp instruction, information can be obtained
-about migration and TSC frequency/offset adjustment to allow the
-vast majority of timestamps to be obtained at top performance; when
-running on a TSC-unsafe processor or a processor that doesn't support
-the rdtscp instruction, rdtscp is emulated.
-
-PVRDTSCP (tsc_mode==3) has two limitations.  First, it applies to
-all apps running in this virtual machine.  This means that all
-apps must either be TSC-resilient or pvrdtscp-modified.  Second,
-highest performance is only obtained on TSC-safe machines that
-support the rdtscp instruction; when running on older machines,
-rdtscp is emulated and thus slower.  For more information on PVRDTSCP,
-see below.
-
 Finally, tsc_mode==1 always enables TSC emulation, regardless of
 the underlying physical hardware. The "apparent" TSC frequency will
 be the TSC frequency of the initial physical machine, even after migration.
@@ -287,56 +261,7 @@ have been replaced by a paravirtualized equivalent of the cpuid instruction
 ("pvcpuid") and also trap to Xen.  But apps in a PV guest that use a
 cpuid instruction execute it directly, without a trap to Xen.  As a result,
 an app may directly examine the physical TSC Invariant cpuid bit and make
-decisions based on that bit.  This is still an unsolved problem, though
-a workaround exists as part of the PVRDTSCP tsc_mode for apps that
-can be modified.
-
-=head1 MORE ON PVRDTSCP
-
-Paravirtualized OS's use the "pvclock" algorithm to manage the passing
-of time.  This sophisticated algorithm obtains information from a memory
-page shared between Xen and the OS and selects information from this
-page based on the current virtual CPU (vcpu) in order to properly adapt to
-TSC-unsafe systems and changes that occur across migration.  Neither
-this shared page nor the vcpu information is available to a userland
-app so the pvclock algorithm cannot be directly used by an app, at least
-without performance degradation roughly equal to the cost of just
-emulating an rdtsc.
-
-As a result, as of 4.0, Xen provides capabilities for a userland app
-to obtain key time values similar to the information accessible
-to the PV OS pvclock algorithm.  The app uses the rdtscp instruction
-which is defined in recent processors to obtain both the TSC and an
-auxiliary value called TSC_AUX.  Xen is responsible for setting TSC_AUX
-to the same value on all vcpus running any domain with tsc_mode==3;
-further, Xen tools are responsible for monotonically incrementing TSC_AUX
-anytime the domain is restored/migrated (thus changing key time values);
-and, when the domain is running on a physical machine that either
-is not TSC-safe or does not support the rdtscp instruction, Xen
-is responsible for emulating the rdtscp instruction and for setting
-TSC_AUX to zero on all processors.
-
-Xen also provides pvclock information via a "pvcpuid" instruction.
-While this results in a slow trap, the information changes
-(and thus must be reobtained via pvcpuid) ONLY when TSC_AUX
-has changed, which should be very rare relative to a high
-frequency of rdtscp instructions.
-
-Finally, Xen provides additional time-related information via
-other pvcpuid instructions.  First, an app is capable of
-determining if it is currently running on Xen, next whether
-the tsc_mode setting of the domain in which it is running,
-and finally whether the underlying hardware is TSC-safe and
-supports the rdtscp instruction.
-
-As a result, a pvrdtscp-modified app has sufficient information
-to compute the pvclock "elapsed nanoseconds" which can
-be used as a timestamp.  And this can be done nearly as
-fast as a native rdtsc instruction, much faster than emulation,
-and also much faster than nearly all OS-provided time mechanisms.
-While pvrtscp is too complex for most apps, certain enterprise
-TSC-sensitive high-TSC-frequency apps may find it useful to
-obtain a significant performance gain.
+decisions based on that bit.
 
 =head1 HARDWARE TSC SCALING
 
@@ -344,21 +269,16 @@ Intel VMX TSC scaling and AMD SVM TSC ratio allow the guest TSC read
 by guest rdtsc/p increasing in a different frequency than the host
 TSC frequency.
 
-If a HVM container in default TSC mode (tsc_mode=0) or PVRDTSCP mode
-(tsc_mode=3) is created on a host that provides constant TSC, its
-guest TSC frequency will be the same as the host. If it is later
-migrated to another host that provides constant TSC and supports Intel
-VMX TSC scaling/AMD SVM TSC ratio, its guest TSC frequency will be the
-same before and after migration.
+If a HVM container in default TSC mode (tsc_mode=0) is created on a host
+that provides constant TSC, its guest TSC frequency will be the same as
+the host. If it is later migrated to another host that provides constant
+TSC and supports Intel VMX TSC scaling/AMD SVM TSC ratio, its guest TSC
+frequency will be the same before and after migration.
 
 For above HVM container in default TSC mode (tsc_mode=0), if above
 hosts support rdtscp, both guest rdtsc and rdtscp instructions will be
 executed natively before and after migration.
 
-For above HVM container in PVRDTSCP mode (tsc_mode=3), if the
-destination host does not support rdtscp, the guest rdtscp instruction
-will be emulated with the guest TSC frequency.
-
 =head1 AUTHORS
 
 Dan Magenheimer <dan.magenheimer@oracle.com>
diff --git a/docs/man/xl.cfg.pod.5.in b/docs/man/xl.cfg.pod.5.in
index b1c0be1..3b92f39 100644
--- a/docs/man/xl.cfg.pod.5.in
+++ b/docs/man/xl.cfg.pod.5.in
@@ -2099,14 +2099,7 @@ by h/w, else executed natively.
 
 =item B<native_paravirt>
 
-Same as B<native>, except Xen manages the TSC_AUX register so the guest can
-determine when a restore/migration has occurred and assumes guest
-obtains/uses a pvclock-like mechanism to adjust for monotonicity and
-frequency changes.
-
-If a HVM container in B<native_paravirt> TSC mode can execute both guest
-rdtsc and guest rdtscp natively, then the guest TSC frequency will be
-determined in a similar way to that of B<default> TSC mode.
+This mode has been removed.
 
 =back
 
diff --git a/docs/misc/pvrdtscp.c b/docs/misc/pvrdtscp.c
deleted file mode 100644
index 8d25843..0000000
--- a/docs/misc/pvrdtscp.c
+++ /dev/null
@@ -1,307 +0,0 @@
-/* pvrdtscp algorithm
- *
- * This sample code demonstrates the use of the paravirtualized rdtscp
- * algorithm.  Using this algorithm, an application may communicate with
- * the Xen hypervisor (version 4.0+) to obtain timestamp information which
- * is both monotonically increasing and has a fixed 1 GHz rate, even across
- * migrations between machines with different TSC rates and offsets.
- * Further,the algorithm provides performance near the performance of a
- * native rdtsc/rdtscp instruction -- much faster than emulation PROVIDED
- * the application is running on a machine on which the rdtscp instruction
- * is supported and TSC is "safe". The application must also be running in a
- * PV domain.  (HVM domains may be supported at a later time.) On machines
- * where TSC is unsafe or the rdtscp instruction is not supported, Xen
- * (v4.0+) provides emulation which is slower but consistent with the pvrdtscp
- * algorithm, thus providing support for the algorithm for live migration
- * across all machines.
- *
- * More information can be found within the Xen (4.0+) source tree at
- *  docs/misc/tscmode.txt
- *
- * Copyright (c) 2009 Oracle Corporation and/or its affiliates.
- * All rights reserved
- * Written by: Dan Magenheimer <dan.magenheimer@oracle.com>
- * 
- * This code is derived from code licensed under the GNU
- * General Public License ("GPL") version 2 and is therefore itself
- * also licensed under the GPL version 2.
- *
- * This code is known to compile and run on Oracle Enterprise Linux 5 Update 2
- * using gcc version 4.1.2, but its purpose is to describe the pvrdtscp
- * algorithm and its ABI to Xen version 4.0+ 
- */
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/wait.h>
-
-#ifdef __LP64__
-#define __X86_64__
-typedef unsigned short u16;
-typedef unsigned int u32;
-typedef unsigned long u64;
-typedef int i32;
-typedef long i64;
-#define NSEC_PER_SEC 1000000000
-#else
-#define __X86_32__
-typedef unsigned int u16;
-typedef unsigned long u32;
-typedef unsigned long long u64;
-typedef long i32;
-typedef long long i64;
-#define NSEC_PER_SEC 1000000000L
-#endif
-
-static inline void hvm_cpuid(u32 idx, u32 sub,
-				u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
-{
-	*eax = idx, *ecx = sub;
-	asm("cpuid" : "=a" (*eax), "=b" (*ebx), "=c" (*ecx), "=d" (*edx)
-	    : "0" (*eax), "2" (*ecx));
-}
-
-static inline void pv_cpuid(u32 idx, u32 sub,
-				u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
-{
-	*eax = idx, *ecx = sub;
-	asm volatile ( "ud2a ; .ascii \"xen\"; cpuid" : "=a" (*eax),
-            "=b" (*ebx), "=c" (*ecx), "=d" (*edx) : "0" (*eax), "2" (*ecx));
-}
-
-static inline u64 do_rdtscp(u32 *aux)
-{
-static u64 last = 0;
-	u32 lo32, hi32;
-	u64 val;
-
-	asm volatile(".byte 0x0f,0x01,0xf9":"=a"(lo32),"=d"(hi32),"=c" (*aux));
-	val = lo32 | ((u64)hi32 << 32);
-	return val;
-}
-
-static inline int get_xen_tsc_mode(void)
-{
-	u32 val, dummy1, dummy2, dummy3;
-	pv_cpuid(0x40000003,0,&dummy1,&val,&dummy2,&dummy3);
-	return val;
-}
-
-static inline int get_xen_vtsc(void)
-{
-	u32 val, dummy1, dummy2, dummy3;
-	pv_cpuid(0x40000003,0,&val,&dummy1,&dummy2,&dummy3);
-	return val & 1;
-}
-
-static inline int get_xen_vtsc_khz(void)
-{
-	u32 val, dummy1, dummy2, dummy3;
-	pv_cpuid(0x40000003,0,&dummy1,&dummy2,&val,&dummy3);
-	return val;
-}
-
-static inline u32 get_xen_cpu_khz(void)
-{
-	u32 cpu_khz, dummy1, dummy2, dummy3;
-	pv_cpuid(0x40000003,2,&cpu_khz,&dummy1,&dummy2,&dummy3);
-	return cpu_khz;
-}
-
-static inline u32 get_xen_incarnation(void)
-{
-	u32 incarn, dummy1, dummy2, dummy3;
-	pv_cpuid(0x40000003,0,&dummy1,&dummy2,&dummy3,&incarn);
-	return incarn;
-}
-
-static inline void get_xen_time_values(u64 *offset, u32 *mul_frac, u32 *shift)
-{
-	u32 off_lo, off_hi, sys_lo, sys_hi, dummy;
-
-	pv_cpuid(0x40000003,1,&off_lo,&off_hi,mul_frac,shift);
-	*offset = off_lo | ((u64)off_hi << 32);
-}
-
-static inline u64 scale_delta(u64 delta, u32 tsc_mul_frac, i32 tsc_shift)
-{
-    u64 product;
-#ifdef __X86_32__
-    u32 tmp1, tmp2;
-#endif
-
-    if ( tsc_shift < 0 )
-        delta >>= -tsc_shift;
-    else
-        delta <<= tsc_shift;
-
-#ifdef __X86_32__
-    asm (
-        "mul  %5       ; "
-        "mov  %4,%%eax ; "
-        "mov  %%edx,%4 ; "
-        "mul  %5       ; "
-        "xor  %5,%5    ; "
-        "add  %4,%%eax ; "
-        "adc  %5,%%edx ; "
-        : "=A" (product), "=r" (tmp1), "=r" (tmp2)
-        : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (tsc_mul_frac) );
-#else
-    asm (
-        "mul %%rdx ; shrd $32,%%rdx,%%rax"
-        : "=a" (product) : "0" (delta), "d" ((u64)tsc_mul_frac) );
-#endif
-
-    return product;
-}
-
-static inline u64 get_pvrdtscp_timestamp(int *discontinuity)
-{
-	static int firsttime = 1;
-	static u64 last_pvrdtscp_timestamp = 0;
-	static u32 last_tsc_aux;
-	static u64 xen_ns_offset;
-	static u32 xen_tsc_to_ns_mul_frac, xen_tsc_to_ns_shift;
-	u32 this_tsc_aux;
-	u64 timestamp, cur_tsc, cur_ns;
-
-	if (firsttime) {
-		cur_tsc = do_rdtscp(&last_tsc_aux);
-		get_xen_time_values(&xen_ns_offset, &xen_tsc_to_ns_mul_frac,
-					&xen_tsc_to_ns_shift);
-		cur_ns = scale_delta(cur_tsc, xen_tsc_to_ns_mul_frac,
-					xen_tsc_to_ns_shift);
-		timestamp = cur_ns - xen_ns_offset;
-		last_pvrdtscp_timestamp = timestamp;
-		firsttime = 0;
-	}
-	cur_tsc = do_rdtscp(&this_tsc_aux);
-	*discontinuity = 0;
-	while (this_tsc_aux != last_tsc_aux) {
-		/* if tsc_aux changed, try again */
-		last_tsc_aux = this_tsc_aux;
-		get_xen_time_values(&xen_ns_offset, &xen_tsc_to_ns_mul_frac,
-					&xen_tsc_to_ns_shift);
-		cur_tsc = do_rdtscp(&this_tsc_aux);
-		*discontinuity = 1;
-	}
-
-	/* compute nsec from TSC and Xen time values */
-	cur_ns = scale_delta(cur_tsc, xen_tsc_to_ns_mul_frac,
-					xen_tsc_to_ns_shift);
-	timestamp = cur_ns - xen_ns_offset;
-
-	/* enforce monotonicity just in case */
-	if ((i64)(timestamp - last_pvrdtscp_timestamp) > 0)
-		last_pvrdtscp_timestamp = timestamp;
-	else {
-		/* this should never happen but we'll check it anyway in
-		 * case of some strange combination of scaling errors
-		 * occurs across a very fast migration */
-		printf("Time went backwards by %lluns\n",
-		    (unsigned long long)(last_pvrdtscp_timestamp-timestamp));
-		timestamp = ++last_pvrdtscp_timestamp;
-	}
-	return timestamp;
-}
-
-#define HVM 1
-#define PVM 0
-
-static int running_on_xen(int hvm, u16 *version_major, u16 *version_minor)
-{
-	u32 eax, ebx, ecx, edx, base;
-	union { char csig[16]; u32 u[4]; } sig;
-
-	for (base=0x40000000; base < 0x40010000; base += 0x100) {
-		if (hvm==HVM)
-			hvm_cpuid(base,0,&eax,&ebx,&ecx,&edx);
-		else
-			pv_cpuid(base,0,&eax,&ebx,&ecx,&edx);
-		sig.u[0] = ebx; sig.u[1] = ecx; sig.u[2] = edx;
-		sig.csig[12] = '\0';
-		if (!strcmp("XenVMMXenVMM",&sig.csig[0]) && (eax >= (base+2))) {
-				if (hvm==HVM)
-					hvm_cpuid(base+1,0,&eax,&ebx,&ecx,&edx);
-				else
-					pv_cpuid(base+1,0,&eax,&ebx,&ecx,&edx);
-				*version_major = (eax >> 16) & 0xffff;
-				*version_minor = eax & 0xffff;
-				return 1;
-		}
-	}
-	return 0;
-}
-
-main(int ac, char **av)
-{
-	u32 dummy;
-	u16 version_hi, version_lo;
-	u64 ts, last_ts;
-	int status, discontinuity = 0;
-	pid_t pid;
-
-	if (running_on_xen(HVM,&version_hi,&version_lo)) {
-		printf("running on Xen v%d.%d as an HVM domain, "
-			"pvrdtsc not supported, exiting\n",
-			(int)version_hi, (int)version_lo);
-		exit(0);
-	}
-	pid = fork();
-	if (pid == -1) {
-		fprintf(stderr,"Huh? Fork failed\n");
-		return 0;
-	}
-	else if (pid == 0) { /* child */
-		pv_cpuid(0x40000000,0,&dummy,&dummy,&dummy,&dummy);
-		exit(0);
-	}
-	waitpid(pid,&status,0);
-	if (!WIFEXITED(status))
-		exit(0);
-	if (!running_on_xen(PVM,&version_hi,&version_lo)) {
-		printf("not running on Xen, exiting\n");
-		exit(0);
-	}
-	printf("running on Xen v%d.%d as a PV domain\n",
-		(int)version_hi, (int)version_lo);
-	if ( version_hi <= 3 ) {
-		printf("pvrdtscp requires Xen version 4.0 or greater\n");
-		/* exit(0); FIXME after xen-unstable is officially v4.0 */
-	}
-	if ( get_xen_tsc_mode() != 3 )
-		printf("tsc_mode not pvrdtscp, set tsc_mode=3, exiting\n");
-
-	/* OK, we are on Xen, now loop forever checking timestamps */
-	ts = get_pvrdtscp_timestamp(&discontinuity);
-	printf("Starting with ts=%lluns 0x%llx (%llusec)\n",ts,ts,ts/NSEC_PER_SEC);
-	printf("incarn=%d: vtsc=%d, vtsc_khz=%lu, phys cpu_khz=%lu\n",
-				(unsigned long)get_xen_incarnation(),
-				(unsigned long)get_xen_vtsc(),
-				(unsigned long)get_xen_vtsc_khz(),
-				(unsigned long)get_xen_cpu_khz());
-	ts = get_pvrdtscp_timestamp(&discontinuity);
-	last_ts = ts;
-	while (1) {
-		ts = get_pvrdtscp_timestamp(&discontinuity);
-		if (discontinuity)
-			printf("migrated/restored, incarn=%d: "
-                               "vtsc now %d, vtsc_khz=%lu, phys cpu_khz=%lu\n",
-				(unsigned long)get_xen_incarnation(),
-				(unsigned long)get_xen_vtsc(),
-				(unsigned long)get_xen_vtsc_khz(),
-				(unsigned long)get_xen_cpu_khz());
-		if (ts < last_ts)
-			/* this should NEVER happen, especially since there
-			 * is a check for it in get_pvrdtscp_timestamp() */
-			printf("Time went backwards: %lluns (%llusec)\n",
-				last_ts-ts,(last_ts-ts)/NSEC_PER_SEC);
-		if (ts > last_ts + 200000000LL)
-			/* this is OK, usually about 2sec for save/restore
-			 * and a fraction of a second for live migrate */
-			printf("Time jumped forward %lluns (%llusec)\n",
-				ts-last_ts,(ts-last_ts)/NSEC_PER_SEC);
-		last_ts = ts;
-	}
-}
diff --git a/tools/libxl/libxl_x86.c b/tools/libxl/libxl_x86.c
index c04fd75..c0f88a7 100644
--- a/tools/libxl/libxl_x86.c
+++ b/tools/libxl/libxl_x86.c
@@ -309,12 +309,19 @@ int libxl__arch_domain_create(libxl__gc *gc, libxl_domain_config *d_config,
         tsc_mode = 2;
         break;
     case LIBXL_TSC_MODE_NATIVE_PARAVIRT:
-        tsc_mode = 3;
-        break;
+        LOGD(ERROR, domid, "TSC Mode native_paravirt (a.k.a PVRDTSCP) has been removed");
+        ret = ERROR_FEATURE_REMOVED;
+        goto out;
     default:
         abort();
     }
-    xc_domain_set_tsc_info(ctx->xch, domid, tsc_mode, 0, 0, 0);
+
+    if (xc_domain_set_tsc_info(ctx->xch, domid, tsc_mode, 0, 0, 0)) {
+        LOGE(ERROR, "xc_domain_set_tsc_info() failed");
+        ret = ERROR_FAIL;
+        goto out;
+    }
+
     if (libxl_defbool_val(d_config->b_info.disable_migrate))
         xc_domain_disable_migrate(ctx->xch, domid);
     rtc_timeoffset = d_config->b_info.rtc_timeoffset;
diff --git a/tools/python/xen/lowlevel/xc/xc.c b/tools/python/xen/lowlevel/xc/xc.c
index 484b790..cc8175a 100644
--- a/tools/python/xen/lowlevel/xc/xc.c
+++ b/tools/python/xen/lowlevel/xc/xc.c
@@ -2439,7 +2439,7 @@ static PyMethodDef pyxc_methods[] = {
       "Set a domain's TSC mode\n"
       " dom        [int]: Domain whose TSC mode is being set.\n"
       " tsc_mode   [int]: 0=default (monotonic, but native where possible)\n"
-      "                   1=always emulate 2=never emulate 3=pvrdtscp\n"
+      "                   1=always emulate 2=never emulate\n"
       "Returns: [int] 0 on success; -1 on error.\n" },
 
     { "domain_disable_migrate",
-- 
2.1.4


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Re: [PATCH v2 6/5] tools/docs: Remove PVRDTSCP remnants

[Jan Beulich]

>>> On 14.12.18 at 01:52, <andrew.cooper3@citrix.com> wrote:
> PVRDTSCP is believed-unused, and its implementation has adverse consequences
> on unrelated functionality in the hypervisor.  As a result, support has been
> removed.
> 
> Modify libxl to provide a slightly more helpful error message if it 
> encounters
> PVRDTSCP being selected.  While adjusting TSC handling, make libxl check for
> errors from the set_tsc hypercall.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> ---
>  docs/man/xen-tscmode.pod.7        |  94 +-----------
>  docs/misc/pvrdtscp.c              | 307 --------------------------------------

Acked-by: Jan Beulich <jbeulich@suse.com>


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Re: [PATCH v2 6/5] tools/docs: Remove PVRDTSCP remnants

[Ian Jackson]

Andrew Cooper writes ("[Xen-devel] [PATCH v2 6/5] tools/docs: Remove PVRDTSCP remnants"):
> PVRDTSCP is believed-unused, and its implementation has adverse consequences
> on unrelated functionality in the hypervisor.  As a result, support has been
> removed.

Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

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