Re: [Qemu-devel] [PATCH v2 4/8] exec: Factor out cpu_watchpoint_address_matches

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 8/29/19 1:16 AM, Richard Henderson wrote:
> We want to move the check for watchpoints from
> memory_region_section_get_iotlb to tlb_set_page_with_attrs.
> Isolate the loop over watchpoints to an exported function.
> 
> Rename the existing cpu_watchpoint_address_matches to
> watchpoint_address_matches, since it doesn't actually
> have a cpu argument.
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  include/hw/core/cpu.h |  7 +++++++
>  exec.c                | 45 ++++++++++++++++++++++++++++---------------
>  2 files changed, 36 insertions(+), 16 deletions(-)
> 
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 7bd8bed5b2..c7cda65c66 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -1096,6 +1096,12 @@ static inline void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
>                                          MemTxAttrs atr, int fl, uintptr_t ra)
>  {
>  }
> +
> +static inline int cpu_watchpoint_address_matches(CPUState *cpu,
> +                                                 vaddr addr, vaddr len)
> +{
> +    return 0;
> +}
>  #else
>  int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len,
>                            int flags, CPUWatchpoint **watchpoint);
> @@ -1105,6 +1111,7 @@ void cpu_watchpoint_remove_by_ref(CPUState *cpu, CPUWatchpoint *watchpoint);
>  void cpu_watchpoint_remove_all(CPUState *cpu, int mask);
>  void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
>                            MemTxAttrs attrs, int flags, uintptr_t ra);
> +int cpu_watchpoint_address_matches(CPUState *cpu, vaddr addr, vaddr len);
>  #endif
>  
>  /**
> diff --git a/exec.c b/exec.c
> index cb6f5763dc..8575ce51ad 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1138,9 +1138,8 @@ void cpu_watchpoint_remove_all(CPUState *cpu, int mask)
>   * partially or completely with the address range covered by the
>   * access).
>   */
> -static inline bool cpu_watchpoint_address_matches(CPUWatchpoint *wp,
> -                                                  vaddr addr,
> -                                                  vaddr len)
> +static inline bool watchpoint_address_matches(CPUWatchpoint *wp,
> +                                              vaddr addr, vaddr len)
>  {
>      /* We know the lengths are non-zero, but a little caution is
>       * required to avoid errors in the case where the range ends
> @@ -1152,6 +1151,20 @@ static inline bool cpu_watchpoint_address_matches(CPUWatchpoint *wp,
>  
>      return !(addr > wpend || wp->vaddr > addrend);
>  }
> +
> +/* Return flags for watchpoints that match addr + prot.  */
> +int cpu_watchpoint_address_matches(CPUState *cpu, vaddr addr, vaddr len)
> +{
> +    CPUWatchpoint *wp;
> +    int ret = 0;
> +
> +    QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
> +        if (watchpoint_address_matches(wp, addr, TARGET_PAGE_SIZE)) {
> +            ret |= wp->flags;
> +        }
> +    }
> +    return ret;
> +}
>  #endif /* !CONFIG_USER_ONLY */
>  
>  /* Add a breakpoint.  */
> @@ -1459,7 +1472,7 @@ hwaddr memory_region_section_get_iotlb(CPUState *cpu,
>                                         target_ulong *address)
>  {
>      hwaddr iotlb;
> -    CPUWatchpoint *wp;
> +    int flags, match;
>  
>      if (memory_region_is_ram(section->mr)) {
>          /* Normal RAM.  */
> @@ -1477,17 +1490,17 @@ hwaddr memory_region_section_get_iotlb(CPUState *cpu,
>          iotlb += xlat;
>      }
>  
> -    /* Make accesses to pages with watchpoints go via the
> -       watchpoint trap routines.  */
> -    QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
> -        if (cpu_watchpoint_address_matches(wp, vaddr, TARGET_PAGE_SIZE)) {
> -            /* Avoid trapping reads of pages with a write breakpoint. */
> -            if ((prot & PAGE_WRITE) || (wp->flags & BP_MEM_READ)) {
> -                iotlb = PHYS_SECTION_WATCH + paddr;
> -                *address |= TLB_MMIO;
> -                break;
> -            }
> -        }
> +    /* Avoid trapping reads of pages with a write breakpoint. */
> +    match = (prot & PAGE_READ ? BP_MEM_READ : 0)
> +          | (prot & PAGE_WRITE ? BP_MEM_WRITE : 0);

Isn't it cheaper to do here:

       if (!match) {
           return iotlb;
       }

or

       if (match) {

> +    flags = cpu_watchpoint_address_matches(cpu, vaddr, TARGET_PAGE_SIZE);
> +    if (flags & match) {
> +        /*
> +         * Make accesses to pages with watchpoints go via the
> +         * watchpoint trap routines.
> +         */
> +        iotlb = PHYS_SECTION_WATCH + paddr;
> +        *address |= TLB_MMIO;
>      }

}

Regardless:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

>      return iotlb;
> @@ -2806,7 +2819,7 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
>  
>      addr = cc->adjust_watchpoint_address(cpu, addr, len);
>      QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
> -        if (cpu_watchpoint_address_matches(wp, addr, len)
> +        if (watchpoint_address_matches(wp, addr, len)
>              && (wp->flags & flags)) {
>              if (flags == BP_MEM_READ) {
>                  wp->flags |= BP_WATCHPOINT_HIT_READ;
>