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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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@xxxxxxxxxx>
Reviewed-by: 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:
 * 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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