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diff --git a/sys/x86/include/pvclock.h b/sys/x86/include/pvclock.h
--- a/sys/x86/include/pvclock.h
+++ b/sys/x86/include/pvclock.h
@@ -121,6 +121,7 @@
/* Private; initialized by the 'pvclock' API: */
bool vdso_force_unstable;
+ bool vdso_enable_without_rdtscp;
struct timecounter tc;
struct cdev *cdev;
};
diff --git a/sys/x86/x86/pvclock.c b/sys/x86/x86/pvclock.c
--- a/sys/x86/x86/pvclock.c
+++ b/sys/x86/x86/pvclock.c
@@ -224,6 +224,9 @@
{
struct pvclock *pvc = tc->tc_priv;
+ if (pvc->cdev == NULL)
+ return (0);
+
vdso_th->th_algo = VDSO_TH_ALGO_X86_PVCLK;
vdso_th->th_x86_shift = 0;
vdso_th->th_x86_hpet_idx = 0;
@@ -232,7 +235,9 @@
vdso_th->th_x86_pvc_stable_mask = !pvc->vdso_force_unstable &&
pvc->stable_flag_supported ? PVCLOCK_FLAG_TSC_STABLE : 0;
bzero(vdso_th->th_res, sizeof(vdso_th->th_res));
- return (pvc->cdev != NULL && amd_feature & AMDID_RDTSCP);
+ return ((amd_feature & AMDID_RDTSCP) != 0 ||
+ ((vdso_th->th_x86_pvc_stable_mask & PVCLOCK_FLAG_TSC_STABLE) != 0 &&
+ pvc->vdso_enable_without_rdtscp));
}
#ifdef COMPAT_FREEBSD32
@@ -242,6 +247,9 @@
{
struct pvclock *pvc = tc->tc_priv;
+ if (pvc->cdev == NULL)
+ return (0);
+
vdso_th->th_algo = VDSO_TH_ALGO_X86_PVCLK;
vdso_th->th_x86_shift = 0;
vdso_th->th_x86_hpet_idx = 0;
@@ -250,7 +258,9 @@
vdso_th->th_x86_pvc_stable_mask = !pvc->vdso_force_unstable &&
pvc->stable_flag_supported ? PVCLOCK_FLAG_TSC_STABLE : 0;
bzero(vdso_th->th_res, sizeof(vdso_th->th_res));
- return (pvc->cdev != NULL && amd_feature & AMDID_RDTSCP);
+ return ((amd_feature & AMDID_RDTSCP) != 0 ||
+ ((vdso_th->th_x86_pvc_stable_mask & PVCLOCK_FLAG_TSC_STABLE) != 0 &&
+ pvc->vdso_enable_without_rdtscp));
}
#endif
@@ -284,6 +294,18 @@
"vdso_force_unstable", CTLFLAG_RW, &pvc->vdso_force_unstable, 0,
"Forcibly deassert stable flag in vDSO codepath");
+ /*
+ * Make it possible to use the vDSO page even when the hypervisor does
+ * not support the rdtscp instruction. This is disabled by default for
+ * compatibility with old libc.
+ */
+ pvc->vdso_enable_without_rdtscp = false;
+ SYSCTL_ADD_BOOL(device_get_sysctl_ctx(dev),
+ SYSCTL_CHILDREN(device_get_sysctl_tree(dev)), OID_AUTO,
+ "vdso_enable_without_rdtscp", CTLFLAG_RWTUN,
+ &pvc->vdso_enable_without_rdtscp, 0,
+ "Allow the use of a vDSO when rdtscp is not available");
+
/* Set up timecounter and timecounter-supporting members: */
pvc->tc.tc_get_timecount = pvclock_tc_get_timecount;
pvc->tc.tc_poll_pps = NULL;

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