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@rasmusvillemoes.dk>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <Waiman.Long@hpe.com>
Cc: Waiman Long <waiman.long@hpe.com>
Link: http://lkml.kernel.org/r/d2f90bba98db9905041cff294646d290d378f67a.1460074438.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index 03c3eb77bfcebce765b838271b6d7789365ff3de..2f02d23a05ef4b20c8a620c9bef4e7943e02ab1f 100644 (file)
--- 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 4158acc17df07c355f0d86e19fd3b4f9b43e590e..a708aa90b507fce048e05676f073f7b9f3347e59 100644 (file)
--- 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 10f704584922653fd208646cac11c4f8a9cd776b..b3cf81333a54edf146c26a747db201111b7863d3 100644 (file)
--- 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 d194266acb28e52d237c19c21291633c15d99c9e..eae33c7170c868993ffc3b861ca30ddc14285aa7 100644 (file)
--- 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 a1f0e4a5c47e3239824ac9c61774127e378d4f03..7282c2e3858ec3fbf236d4790ae917ca05815ed2 100644 (file)
--- 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 2f1ea2f61e1fceef4a77b3955c4d3a9c4a936a72..b72743c5668d3d55387a55d06c0c886cf2b7b1b1 100644 (file)
--- 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),