[tip:x86/asm] x86/vdso: Remove direct HPET access through the vDSO

From: tip-bot for Andy Lutomirski
Date: Wed Apr 13 2016 - 07:32:42 EST

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Commit-ID: 1ed95e52d902035e39a715ff3a314a893a96e5b7
Gitweb: http://git.kernel.org/tip/1ed95e52d902035e39a715ff3a314a893a96e5b7
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Thu, 7 Apr 2016 17:16:59 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 13 Apr 2016 10:28:34 +0200

x86/vdso: Remove direct HPET access through the vDSO

Allowing user code to map the HPET is problematic. HPET
implementations are notoriously buggy, and there are probably many
machines on which even MMIO reads from bogus HPET addresses are
problematic.

We have a report that the Dell Precision M2800 with:

ACPI: HPET 0x00000000C8FE6238 000038 (v01 DELL CBX3 01072009 AMI. 00000005)

is either so slow when accessing the HPET or actually hangs in some
regard, causing soft lockups to be reported if users do unexpected
things to the HPET.

The vclock HPET code has also always been a questionable speedup.
Accessing an HPET is exceedingly slow (on the order of several
microseconds), so the added overhead in requiring a syscall to read
the HPET is a small fraction of the total code of accessing it.

To avoid future problems, let's just delete the code entirely.

In the long run, this could actually be a speedup. Waiman Long as a
patch to optimize the case where multiple CPUs contend for the HPET,
but that won't help unless all the accesses are mediated by the
kernel.

Reported-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxxx>
Cc: Waiman Long <waiman.long@xxxxxxx>
Link: http://lkml.kernel.org/r/d2f90bba98db9905041cff294646d290d378f67a.1460074438.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/entry/vdso/vclock_gettime.c | 15 ---------------
arch/x86/entry/vdso/vdso-layout.lds.S | 5 ++---
arch/x86/entry/vdso/vma.c | 11 -----------
arch/x86/include/asm/clocksource.h | 9 ++++-----
arch/x86/kernel/hpet.c | 1 -
arch/x86/kvm/trace.h | 3 +--
6 files changed, 7 insertions(+), 37 deletions(-)

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index 03c3eb7..2f02d23 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -13,7 +13,6 @@

#include <uapi/linux/time.h>
#include <asm/vgtod.h>
-#include <asm/hpet.h>
#include <asm/vvar.h>
#include <asm/unistd.h>
#include <asm/msr.h>
@@ -28,16 +27,6 @@ extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
extern time_t __vdso_time(time_t *t);

-#ifdef CONFIG_HPET_TIMER
-extern u8 hpet_page
- __attribute__((visibility("hidden")));
-
-static notrace cycle_t vread_hpet(void)
-{
- return *(const volatile u32 *)(&hpet_page + HPET_COUNTER);
-}
-#endif
-
#ifdef CONFIG_PARAVIRT_CLOCK
extern u8 pvclock_page
__attribute__((visibility("hidden")));
@@ -195,10 +184,6 @@ notrace static inline u64 vgetsns(int *mode)

if (gtod->vclock_mode == VCLOCK_TSC)
cycles = vread_tsc();
-#ifdef CONFIG_HPET_TIMER
- else if (gtod->vclock_mode == VCLOCK_HPET)
- cycles = vread_hpet();
-#endif
#ifdef CONFIG_PARAVIRT_CLOCK
else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
cycles = vread_pvclock(mode);
diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index 4158acc..a708aa9 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -25,7 +25,7 @@ SECTIONS
* segment.
*/

- vvar_start = . - 3 * PAGE_SIZE;
+ vvar_start = . - 2 * PAGE_SIZE;
vvar_page = vvar_start;

/* Place all vvars at the offsets in asm/vvar.h. */
@@ -35,8 +35,7 @@ SECTIONS
#undef __VVAR_KERNEL_LDS
#undef EMIT_VVAR

- hpet_page = vvar_start + PAGE_SIZE;
- pvclock_page = vvar_start + 2 * PAGE_SIZE;
+ pvclock_page = vvar_start + PAGE_SIZE;

. = SIZEOF_HEADERS;

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 10f7045..b3cf813 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -18,7 +18,6 @@
#include <asm/vdso.h>
#include <asm/vvar.h>
#include <asm/page.h>
-#include <asm/hpet.h>
#include <asm/desc.h>
#include <asm/cpufeature.h>

@@ -129,16 +128,6 @@ static int vvar_fault(const struct vm_special_mapping *sm,
if (sym_offset == image->sym_vvar_page) {
ret = vm_insert_pfn(vma, (unsigned long)vmf->virtual_address,
__pa_symbol(&__vvar_page) >> PAGE_SHIFT);
- } else if (sym_offset == image->sym_hpet_page) {
-#ifdef CONFIG_HPET_TIMER
- if (hpet_address && vclock_was_used(VCLOCK_HPET)) {
- ret = vm_insert_pfn_prot(
- vma,
- (unsigned long)vmf->virtual_address,
- hpet_address >> PAGE_SHIFT,
- pgprot_noncached(PAGE_READONLY));
- }
-#endif
} else if (sym_offset == image->sym_pvclock_page) {
struct pvclock_vsyscall_time_info *pvti =
pvclock_pvti_cpu0_va();
diff --git a/arch/x86/include/asm/clocksource.h b/arch/x86/include/asm/clocksource.h
index d194266..eae33c7 100644
--- a/arch/x86/include/asm/clocksource.h
+++ b/arch/x86/include/asm/clocksource.h
@@ -3,11 +3,10 @@
#ifndef _ASM_X86_CLOCKSOURCE_H
#define _ASM_X86_CLOCKSOURCE_H

-#define VCLOCK_NONE 0 /* No vDSO clock available. */
-#define VCLOCK_TSC 1 /* vDSO should use vread_tsc. */
-#define VCLOCK_HPET 2 /* vDSO should use vread_hpet. */
-#define VCLOCK_PVCLOCK 3 /* vDSO should use vread_pvclock. */
-#define VCLOCK_MAX 3
+#define VCLOCK_NONE 0 /* No vDSO clock available. */
+#define VCLOCK_TSC 1 /* vDSO should use vread_tsc. */
+#define VCLOCK_PVCLOCK 2 /* vDSO should use vread_pvclock. */
+#define VCLOCK_MAX 2

struct arch_clocksource_data {
int vclock_mode;
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index a1f0e4a..7282c2e 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -773,7 +773,6 @@ static struct clocksource clocksource_hpet = {
.mask = HPET_MASK,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
.resume = hpet_resume_counter,
- .archdata = { .vclock_mode = VCLOCK_HPET },
};

static int hpet_clocksource_register(void)
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 2f1ea2f..b72743c 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -809,8 +809,7 @@ TRACE_EVENT(kvm_write_tsc_offset,

#define host_clocks \
{VCLOCK_NONE, "none"}, \
- {VCLOCK_TSC, "tsc"}, \
- {VCLOCK_HPET, "hpet"} \
+ {VCLOCK_TSC, "tsc"} \

TRACE_EVENT(kvm_update_master_clock,
TP_PROTO(bool use_master_clock, unsigned int host_clock, bool offset_matched),

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