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Allow the kernel to emulate the physical counter on arm64

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When running under a VM we don't have access to the physical counter.
Add support to emulate this instruction by handling the trap in the
kernel. As it is slow only enable when the hw.emulate_phys_counter
tunable is set on boot.

Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D35613
This commit is contained in:
Andrew Turner 2022-06-27 12:37:40 +00:00
parent 2aba6e7aaf
commit 278111b8a5
1 changed files with 45 additions and 1 deletions
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46
sys/arm/arm/generic_timer.c
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@ -63,6 +63,10 @@ __FBSDID("$FreeBSD$");
#include <machine/machdep.h> /* For arm_set_delay */
#endif
#if defined(__aarch64__)
#include <machine/undefined.h>
#endif
#ifdef FDT
#include <dev/ofw/openfirm.h>
#include <dev/ofw/ofw_bus.h>
@ -235,12 +239,52 @@ setup_user_access(void *arg __unused)
isb();
}
#ifdef __aarch64__
static int
cntpct_handler(vm_offset_t va, uint32_t insn, struct trapframe *frame,
uint32_t esr)
{
uint64_t val;
int reg;
if ((insn & MRS_MASK) != MRS_VALUE)
return (0);
if (MRS_SPECIAL(insn) != MRS_SPECIAL(CNTPCT_EL0))
return (0);
reg = MRS_REGISTER(insn);
val = READ_SPECIALREG(cntvct_el0);
if (reg < nitems(frame->tf_x)) {
frame->tf_x[reg] = val;
} else if (reg == 30) {
frame->tf_lr = val;
}
/*
* We will handle this instruction, move to the next so we
* don't trap here again.
*/
frame->tf_elr += INSN_SIZE;
return (1);
}
#endif
static void
tmr_setup_user_access(void *arg __unused)
{
int emulate;
if (arm_tmr_sc != NULL)
if (arm_tmr_sc != NULL) {
smp_rendezvous(NULL, setup_user_access, NULL, NULL);
#ifdef __aarch64__
if (TUNABLE_INT_FETCH("hw.emulate_phys_counter", &emulate) &&
emulate != 0) {
install_undef_handler(true, cntpct_handler);
}
#endif
}
}
SYSINIT(tmr_ua, SI_SUB_SMP, SI_ORDER_ANY, tmr_setup_user_access, NULL);