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Re: [Xen-devel] [PATCH LINUX v4] xen: event channel arrays are xen_ulong_t and not unsigned long



On Tue, Feb 19, 2013 at 05:29:11PM +0000, Ian Campbell wrote:
> On ARM we want these to be the same size on 32- and 64-bit.
> 
> This is an ABI change on ARM. X86 does not change.

Hehe. You didn't test this, did you :-)

It hangs bootup on X86.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Jan Beulich <JBeulich@xxxxxxxx>
> Cc: Keir (Xen.org) <keir@xxxxxxx>
> Cc: Tim Deegan <tim@xxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxx
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> Changes since V3
>   s/read_evtchn_pending_sel/xchg_xen_ulong/ in a comment.
> Changes since V2
>   Add comments about the correct bitops to use, and on the ordering/barrier
>   requirements on xchg_xen_ulong.
> Changes since V1
>   use find_first_set not __ffs
>   fix some more unsigned long -> xen_ulong_t
>   use more generic xchg_xen_ulong instead of ...read_evtchn...
> ---
>  arch/arm/include/asm/xen/events.h |   22 +++++++
>  arch/x86/include/asm/xen/events.h |    3 +
>  drivers/xen/events.c              |  113 
> +++++++++++++++++++++----------------
>  include/xen/interface/xen.h       |    8 +-
>  4 files changed, 94 insertions(+), 52 deletions(-)
> 
> diff --git a/arch/arm/include/asm/xen/events.h 
> b/arch/arm/include/asm/xen/events.h
> index 94b4e90..5c27696 100644
> --- a/arch/arm/include/asm/xen/events.h
> +++ b/arch/arm/include/asm/xen/events.h
> @@ -15,4 +15,26 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
>       return raw_irqs_disabled_flags(regs->ARM_cpsr);
>  }
>  
> +/*
> + * We cannot use xchg because it does not support 8-byte
> + * values. However it is safe to use {ldr,dtd}exd directly because all
> + * platforms which Xen can run on support those instructions.
> + */
> +static inline xen_ulong_t xchg_xen_ulong(xen_ulong_t *ptr, xen_ulong_t val)
> +{
> +     xen_ulong_t oldval;
> +     unsigned int tmp;
> +
> +     wmb();
> +     asm volatile("@ xchg_xen_ulong\n"
> +             "1:     ldrexd  %0, %H0, [%3]\n"
> +             "       strexd  %1, %2, %H2, [%3]\n"
> +             "       teq     %1, #0\n"
> +             "       bne     1b"
> +             : "=&r" (oldval), "=&r" (tmp)
> +             : "r" (val), "r" (ptr)
> +             : "memory", "cc");
> +     return oldval;
> +}
> +
>  #endif /* _ASM_ARM_XEN_EVENTS_H */
> diff --git a/arch/x86/include/asm/xen/events.h 
> b/arch/x86/include/asm/xen/events.h
> index cc146d5..ca842f2 100644
> --- a/arch/x86/include/asm/xen/events.h
> +++ b/arch/x86/include/asm/xen/events.h
> @@ -16,4 +16,7 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
>       return raw_irqs_disabled_flags(regs->flags);
>  }
>  
> +/* No need for a barrier -- XCHG is a barrier on x86. */
> +#define xchg_xen_ulong(ptr, val) xchg((ptr), (val))
> +
>  #endif /* _ASM_X86_XEN_EVENTS_H */
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index 0be4df3..b8d84f5 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -80,6 +80,12 @@ enum xen_irq_type {
>  };
>  
>  /*
> + * Make a bitmask (i.e. unsigned long *) of a xen_ulong_t
> + * array. Primarily to avoid long lines (hence the terse name).
> + */
> +#define BM(x) (unsigned long *)(x)
> +
> +/*
>   * Packed IRQ information:
>   * type - enum xen_irq_type
>   * event channel - irq->event channel mapping
> @@ -120,7 +126,14 @@ static unsigned long *pirq_eoi_map;
>  #endif
>  static bool (*pirq_needs_eoi)(unsigned irq);
>  
> -static DEFINE_PER_CPU(unsigned long [NR_EVENT_CHANNELS/BITS_PER_LONG],
> +/*
> + * Note sizeof(xen_ulong_t) can be more than sizeof(unsigned long). Be
> + * careful to only use bitops which allow for this (e.g test_bit and
> + * friends but not __ffs).
> + */
> +#define BITS_PER_EVTCHN_WORD (sizeof(xen_ulong_t)*8)
> +
> +static DEFINE_PER_CPU(xen_ulong_t [NR_EVENT_CHANNELS/BITS_PER_EVTCHN_WORD],
>                     cpu_evtchn_mask);
>  
>  /* Xen will never allocate port zero for any purpose. */
> @@ -294,9 +307,9 @@ static bool pirq_needs_eoi_flag(unsigned irq)
>       return info->u.pirq.flags & PIRQ_NEEDS_EOI;
>  }
>  
> -static inline unsigned long active_evtchns(unsigned int cpu,
> -                                        struct shared_info *sh,
> -                                        unsigned int idx)
> +static inline xen_ulong_t active_evtchns(unsigned int cpu,
> +                                      struct shared_info *sh,
> +                                      unsigned int idx)
>  {
>       return sh->evtchn_pending[idx] &
>               per_cpu(cpu_evtchn_mask, cpu)[idx] &
> @@ -312,8 +325,8 @@ static void bind_evtchn_to_cpu(unsigned int chn, unsigned 
> int cpu)
>       cpumask_copy(irq_to_desc(irq)->irq_data.affinity, cpumask_of(cpu));
>  #endif
>  
> -     clear_bit(chn, per_cpu(cpu_evtchn_mask, cpu_from_irq(irq)));
> -     set_bit(chn, per_cpu(cpu_evtchn_mask, cpu));
> +     clear_bit(chn, BM(per_cpu(cpu_evtchn_mask, cpu_from_irq(irq))));
> +     set_bit(chn, BM(per_cpu(cpu_evtchn_mask, cpu)));
>  
>       info_for_irq(irq)->cpu = cpu;
>  }
> @@ -339,19 +352,19 @@ static void init_evtchn_cpu_bindings(void)
>  static inline void clear_evtchn(int port)
>  {
>       struct shared_info *s = HYPERVISOR_shared_info;
> -     sync_clear_bit(port, &s->evtchn_pending[0]);
> +     sync_clear_bit(port, BM(&s->evtchn_pending[0]));
>  }
>  
>  static inline void set_evtchn(int port)
>  {
>       struct shared_info *s = HYPERVISOR_shared_info;
> -     sync_set_bit(port, &s->evtchn_pending[0]);
> +     sync_set_bit(port, BM(&s->evtchn_pending[0]));
>  }
>  
>  static inline int test_evtchn(int port)
>  {
>       struct shared_info *s = HYPERVISOR_shared_info;
> -     return sync_test_bit(port, &s->evtchn_pending[0]);
> +     return sync_test_bit(port, BM(&s->evtchn_pending[0]));
>  }
>  
>  
> @@ -375,7 +388,7 @@ EXPORT_SYMBOL_GPL(notify_remote_via_irq);
>  static void mask_evtchn(int port)
>  {
>       struct shared_info *s = HYPERVISOR_shared_info;
> -     sync_set_bit(port, &s->evtchn_mask[0]);
> +     sync_set_bit(port, BM(&s->evtchn_mask[0]));
>  }
>  
>  static void unmask_evtchn(int port)
> @@ -389,7 +402,7 @@ static void unmask_evtchn(int port)
>       if (unlikely((cpu != cpu_from_evtchn(port))))
>               do_hypercall = 1;
>       else
> -             evtchn_pending = sync_test_bit(port, &s->evtchn_pending[0]);
> +             evtchn_pending = sync_test_bit(port, BM(&s->evtchn_pending[0]));
>  
>       if (unlikely(evtchn_pending && xen_hvm_domain()))
>               do_hypercall = 1;
> @@ -403,7 +416,7 @@ static void unmask_evtchn(int port)
>       } else {
>               struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu);
>  
> -             sync_clear_bit(port, &s->evtchn_mask[0]);
> +             sync_clear_bit(port, BM(&s->evtchn_mask[0]));
>  
>               /*
>                * The following is basically the equivalent of
> @@ -411,8 +424,8 @@ static void unmask_evtchn(int port)
>                * the interrupt edge' if the channel is masked.
>                */
>               if (evtchn_pending &&
> -                 !sync_test_and_set_bit(port / BITS_PER_LONG,
> -                                        &vcpu_info->evtchn_pending_sel))
> +                 !sync_test_and_set_bit(port / BITS_PER_EVTCHN_WORD,
> +                                        BM(&vcpu_info->evtchn_pending_sel)))
>                       vcpu_info->evtchn_upcall_pending = 1;
>       }
>  
> @@ -1189,7 +1202,7 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id)
>  {
>       struct shared_info *sh = HYPERVISOR_shared_info;
>       int cpu = smp_processor_id();
> -     unsigned long *cpu_evtchn = per_cpu(cpu_evtchn_mask, cpu);
> +     xen_ulong_t *cpu_evtchn = per_cpu(cpu_evtchn_mask, cpu);
>       int i;
>       unsigned long flags;
>       static DEFINE_SPINLOCK(debug_lock);
> @@ -1205,7 +1218,7 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id)
>               pending = (get_irq_regs() && i == cpu)
>                       ? xen_irqs_disabled(get_irq_regs())
>                       : v->evtchn_upcall_mask;
> -             printk("%d: masked=%d pending=%d event_sel %0*lx\n  ", i,
> +             printk("%d: masked=%d pending=%d event_sel %0*"PRI_xen_ulong"\n 
>  ", i,
>                      pending, v->evtchn_upcall_pending,
>                      (int)(sizeof(v->evtchn_pending_sel)*2),
>                      v->evtchn_pending_sel);
> @@ -1214,49 +1227,52 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id)
>  
>       printk("\npending:\n   ");
>       for (i = ARRAY_SIZE(sh->evtchn_pending)-1; i >= 0; i--)
> -             printk("%0*lx%s", (int)sizeof(sh->evtchn_pending[0])*2,
> +             printk("%0*"PRI_xen_ulong"%s",
> +                    (int)sizeof(sh->evtchn_pending[0])*2,
>                      sh->evtchn_pending[i],
>                      i % 8 == 0 ? "\n   " : " ");
>       printk("\nglobal mask:\n   ");
>       for (i = ARRAY_SIZE(sh->evtchn_mask)-1; i >= 0; i--)
> -             printk("%0*lx%s",
> +             printk("%0*"PRI_xen_ulong"%s",
>                      (int)(sizeof(sh->evtchn_mask[0])*2),
>                      sh->evtchn_mask[i],
>                      i % 8 == 0 ? "\n   " : " ");
>  
>       printk("\nglobally unmasked:\n   ");
>       for (i = ARRAY_SIZE(sh->evtchn_mask)-1; i >= 0; i--)
> -             printk("%0*lx%s", (int)(sizeof(sh->evtchn_mask[0])*2),
> +             printk("%0*"PRI_xen_ulong"%s",
> +                    (int)(sizeof(sh->evtchn_mask[0])*2),
>                      sh->evtchn_pending[i] & ~sh->evtchn_mask[i],
>                      i % 8 == 0 ? "\n   " : " ");
>  
>       printk("\nlocal cpu%d mask:\n   ", cpu);
> -     for (i = (NR_EVENT_CHANNELS/BITS_PER_LONG)-1; i >= 0; i--)
> -             printk("%0*lx%s", (int)(sizeof(cpu_evtchn[0])*2),
> +     for (i = (NR_EVENT_CHANNELS/BITS_PER_EVTCHN_WORD)-1; i >= 0; i--)
> +             printk("%0*"PRI_xen_ulong"%s", (int)(sizeof(cpu_evtchn[0])*2),
>                      cpu_evtchn[i],
>                      i % 8 == 0 ? "\n   " : " ");
>  
>       printk("\nlocally unmasked:\n   ");
>       for (i = ARRAY_SIZE(sh->evtchn_mask)-1; i >= 0; i--) {
> -             unsigned long pending = sh->evtchn_pending[i]
> +             xen_ulong_t pending = sh->evtchn_pending[i]
>                       & ~sh->evtchn_mask[i]
>                       & cpu_evtchn[i];
> -             printk("%0*lx%s", (int)(sizeof(sh->evtchn_mask[0])*2),
> +             printk("%0*"PRI_xen_ulong"%s",
> +                    (int)(sizeof(sh->evtchn_mask[0])*2),
>                      pending, i % 8 == 0 ? "\n   " : " ");
>       }
>  
>       printk("\npending list:\n");
>       for (i = 0; i < NR_EVENT_CHANNELS; i++) {
> -             if (sync_test_bit(i, sh->evtchn_pending)) {
> -                     int word_idx = i / BITS_PER_LONG;
> +             if (sync_test_bit(i, BM(sh->evtchn_pending))) {
> +                     int word_idx = i / BITS_PER_EVTCHN_WORD;
>                       printk("  %d: event %d -> irq %d%s%s%s\n",
>                              cpu_from_evtchn(i), i,
>                              evtchn_to_irq[i],
> -                            sync_test_bit(word_idx, &v->evtchn_pending_sel)
> +                            sync_test_bit(word_idx, 
> BM(&v->evtchn_pending_sel))
>                                            ? "" : " l2-clear",
> -                            !sync_test_bit(i, sh->evtchn_mask)
> +                            !sync_test_bit(i, BM(sh->evtchn_mask))
>                                            ? "" : " globally-masked",
> -                            sync_test_bit(i, cpu_evtchn)
> +                            sync_test_bit(i, BM(cpu_evtchn))
>                                            ? "" : " locally-masked");
>               }
>       }
> @@ -1273,7 +1289,7 @@ static DEFINE_PER_CPU(unsigned int, current_bit_idx);
>  /*
>   * Mask out the i least significant bits of w
>   */
> -#define MASK_LSBS(w, i) (w & ((~0UL) << i))
> +#define MASK_LSBS(w, i) (w & ((~((xen_ulong_t)0UL)) << i))
>  
>  /*
>   * Search the CPUs pending events bitmasks.  For each one found, map
> @@ -1295,18 +1311,19 @@ static void __xen_evtchn_do_upcall(void)
>       unsigned count;
>  
>       do {
> -             unsigned long pending_words;
> +             xen_ulong_t pending_words;
>  
>               vcpu_info->evtchn_upcall_pending = 0;
>  
>               if (__this_cpu_inc_return(xed_nesting_count) - 1)
>                       goto out;
>  
> -#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
> -             /* Clear master flag /before/ clearing selector flag. */
> -             wmb();
> -#endif
> -             pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
> +             /*
> +              * Master flag must be /before/ clearing selector
> +              * flag. xchg_xen_ulong must contain an appropriate
> +              * barrier.
> +              */
> +             pending_words = xchg_xen_ulong(&vcpu_info->evtchn_pending_sel, 
> 0);
>  
>               start_word_idx = __this_cpu_read(current_word_idx);
>               start_bit_idx = __this_cpu_read(current_bit_idx);
> @@ -1314,8 +1331,8 @@ static void __xen_evtchn_do_upcall(void)
>               word_idx = start_word_idx;
>  
>               for (i = 0; pending_words != 0; i++) {
> -                     unsigned long pending_bits;
> -                     unsigned long words;
> +                     xen_ulong_t pending_bits;
> +                     xen_ulong_t words;
>  
>                       words = MASK_LSBS(pending_words, word_idx);
>  
> @@ -1327,7 +1344,7 @@ static void __xen_evtchn_do_upcall(void)
>                               bit_idx = 0;
>                               continue;
>                       }
> -                     word_idx = __ffs(words);
> +                     word_idx = find_first_bit(BM(&words), sizeof(words));
>  
>                       pending_bits = active_evtchns(cpu, s, word_idx);
>                       bit_idx = 0; /* usually scan entire word from start */
> @@ -1342,7 +1359,7 @@ static void __xen_evtchn_do_upcall(void)
>                       }
>  
>                       do {
> -                             unsigned long bits;
> +                             xen_ulong_t bits;
>                               int port, irq;
>                               struct irq_desc *desc;
>  
> @@ -1352,10 +1369,10 @@ static void __xen_evtchn_do_upcall(void)
>                               if (bits == 0)
>                                       break;
>  
> -                             bit_idx = __ffs(bits);
> +                             bit_idx = find_first_bit(BM(&bits), 
> sizeof(bits));
>  
>                               /* Process port. */
> -                             port = (word_idx * BITS_PER_LONG) + bit_idx;
> +                             port = (word_idx * BITS_PER_EVTCHN_WORD) + 
> bit_idx;
>                               irq = evtchn_to_irq[port];
>  
>                               if (irq != -1) {
> @@ -1364,12 +1381,12 @@ static void __xen_evtchn_do_upcall(void)
>                                               generic_handle_irq_desc(irq, 
> desc);
>                               }
>  
> -                             bit_idx = (bit_idx + 1) % BITS_PER_LONG;
> +                             bit_idx = (bit_idx + 1) % BITS_PER_EVTCHN_WORD;
>  
>                               /* Next caller starts at last processed + 1 */
>                               __this_cpu_write(current_word_idx,
>                                                bit_idx ? word_idx :
> -                                              (word_idx+1) % BITS_PER_LONG);
> +                                              (word_idx+1) % 
> BITS_PER_EVTCHN_WORD);
>                               __this_cpu_write(current_bit_idx, bit_idx);
>                       } while (bit_idx != 0);
>  
> @@ -1377,7 +1394,7 @@ static void __xen_evtchn_do_upcall(void)
>                       if ((word_idx != start_word_idx) || (i != 0))
>                               pending_words &= ~(1UL << word_idx);
>  
> -                     word_idx = (word_idx + 1) % BITS_PER_LONG;
> +                     word_idx = (word_idx + 1) % BITS_PER_EVTCHN_WORD;
>               }
>  
>               BUG_ON(!irqs_disabled());
> @@ -1487,8 +1504,8 @@ int resend_irq_on_evtchn(unsigned int irq)
>       if (!VALID_EVTCHN(evtchn))
>               return 1;
>  
> -     masked = sync_test_and_set_bit(evtchn, s->evtchn_mask);
> -     sync_set_bit(evtchn, s->evtchn_pending);
> +     masked = sync_test_and_set_bit(evtchn, BM(s->evtchn_mask));
> +     sync_set_bit(evtchn, BM(s->evtchn_pending));
>       if (!masked)
>               unmask_evtchn(evtchn);
>  
> @@ -1536,8 +1553,8 @@ static int retrigger_dynirq(struct irq_data *data)
>       if (VALID_EVTCHN(evtchn)) {
>               int masked;
>  
> -             masked = sync_test_and_set_bit(evtchn, sh->evtchn_mask);
> -             sync_set_bit(evtchn, sh->evtchn_pending);
> +             masked = sync_test_and_set_bit(evtchn, BM(sh->evtchn_mask));
> +             sync_set_bit(evtchn, BM(sh->evtchn_pending));
>               if (!masked)
>                       unmask_evtchn(evtchn);
>               ret = 1;
> diff --git a/include/xen/interface/xen.h b/include/xen/interface/xen.h
> index 5d6c272..a9075df 100644
> --- a/include/xen/interface/xen.h
> +++ b/include/xen/interface/xen.h
> @@ -285,7 +285,7 @@ DEFINE_GUEST_HANDLE_STRUCT(multicall_entry);
>   * Event channel endpoints per domain:
>   *  1024 if a long is 32 bits; 4096 if a long is 64 bits.
>   */
> -#define NR_EVENT_CHANNELS (sizeof(unsigned long) * sizeof(unsigned long) * 
> 64)
> +#define NR_EVENT_CHANNELS (sizeof(xen_ulong_t) * sizeof(xen_ulong_t) * 64)
>  
>  struct vcpu_time_info {
>       /*
> @@ -341,7 +341,7 @@ struct vcpu_info {
>        */
>       uint8_t evtchn_upcall_pending;
>       uint8_t evtchn_upcall_mask;
> -     unsigned long evtchn_pending_sel;
> +     xen_ulong_t evtchn_pending_sel;
>       struct arch_vcpu_info arch;
>       struct pvclock_vcpu_time_info time;
>  }; /* 64 bytes (x86) */
> @@ -384,8 +384,8 @@ struct shared_info {
>        * per-vcpu selector word to be set. Each bit in the selector covers a
>        * 'C long' in the PENDING bitfield array.
>        */
> -     unsigned long evtchn_pending[sizeof(unsigned long) * 8];
> -     unsigned long evtchn_mask[sizeof(unsigned long) * 8];
> +     xen_ulong_t evtchn_pending[sizeof(xen_ulong_t) * 8];
> +     xen_ulong_t evtchn_mask[sizeof(xen_ulong_t) * 8];
>  
>       /*
>        * Wallclock time: updated only by control software. Guests should base
> -- 
> 1.7.2.5
> 

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