Re: [Qemu-devel] [RFC v7 01/16] exec.c: Add new exclusive bitmap to ram_list

["Alex Bennée" <alex.bennee@linaro.org>]

Alvise Rigo <a.rigo@virtualopensystems.com> writes:

> The purpose of this new bitmap is to flag the memory pages that are in
> the middle of LL/SC operations (after a LL, before a SC). For all these
> pages, the corresponding TLB entries will be generated in such a way to
> force the slow-path for all the VCPUs (see the following patches).
>
> When the system starts, the whole memory is set to dirty.
>
> Suggested-by: Jani Kokkonen <jani.kokkonen@huawei.com>
> Suggested-by: Claudio Fontana <claudio.fontana@huawei.com>
> Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
> ---
>  exec.c                  |  7 +++++--
>  include/exec/memory.h   |  3 ++-
>  include/exec/ram_addr.h | 31 +++++++++++++++++++++++++++++++
>  3 files changed, 38 insertions(+), 3 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 7115403..51f366d 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1575,11 +1575,14 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp)
>          int i;
>
>          /* ram_list.dirty_memory[] is protected by the iothread lock.  */
> -        for (i = 0; i < DIRTY_MEMORY_NUM; i++) {
> +        for (i = 0; i < DIRTY_MEMORY_EXCLUSIVE; i++) {
>              ram_list.dirty_memory[i] =
>                  bitmap_zero_extend(ram_list.dirty_memory[i],
>                                     old_ram_size, new_ram_size);
> -       }
> +        }
> +        ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE] =
> +            bitmap_zero_extend(ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE],
> +                               old_ram_size, new_ram_size);

In the previous patch you moved this out of the loop as
ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE] was a different size to
the other dirty bitmaps. This no longer seems to be the case so this
seems pointless.

>      }
>      cpu_physical_memory_set_dirty_range(new_block->offset,
>                                          new_block->used_length,
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index c92734a..71e0480 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -19,7 +19,8 @@
>  #define DIRTY_MEMORY_VGA       0
>  #define DIRTY_MEMORY_CODE      1
>  #define DIRTY_MEMORY_MIGRATION 2
> -#define DIRTY_MEMORY_NUM       3        /* num of dirty bits */
> +#define DIRTY_MEMORY_EXCLUSIVE 3
> +#define DIRTY_MEMORY_NUM       4        /* num of dirty bits */
>
>  #include <stdint.h>
>  #include <stdbool.h>
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index ef1489d..19789fc 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -21,6 +21,7 @@
>
>  #ifndef CONFIG_USER_ONLY
>  #include "hw/xen/xen.h"
> +#include "sysemu/sysemu.h"
>
>  struct RAMBlock {
>      struct rcu_head rcu;
> @@ -172,6 +173,9 @@ static inline void cpu_physical_memory_set_dirty_range(ram_addr_t start,
>      if (unlikely(mask & (1 << DIRTY_MEMORY_CODE))) {
>          bitmap_set_atomic(d[DIRTY_MEMORY_CODE], page, end - page);
>      }
> +    if (unlikely(mask & (1 << DIRTY_MEMORY_EXCLUSIVE))) {
> +        bitmap_set_atomic(d[DIRTY_MEMORY_EXCLUSIVE], page, end - page);
> +    }
>      xen_modified_memory(start, length);
>  }
>
> @@ -287,5 +291,32 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(unsigned long *dest,
>  }
>
>  void migration_bitmap_extend(ram_addr_t old, ram_addr_t new);
> +
> +/* Exclusive bitmap support. */
> +#define EXCL_BITMAP_GET_OFFSET(addr) (addr >> TARGET_PAGE_BITS)
> +
> +/* Make the page of @addr not exclusive. */
> +static inline void cpu_physical_memory_unset_excl(ram_addr_t addr)
> +{
> +    set_bit_atomic(EXCL_BITMAP_GET_OFFSET(addr),
> +                   ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE]);
> +}
> +
> +/* Return true if the page of @addr is exclusive, i.e. the EXCL bit is set. */
> +static inline int cpu_physical_memory_is_excl(ram_addr_t addr)
> +{
> +    return !test_bit(EXCL_BITMAP_GET_OFFSET(addr),
> +                     ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE]);
> +}
> +
> +/* Set the page of @addr as exclusive clearing its EXCL bit and return the
> + * previous bit's state. */
> +static inline int cpu_physical_memory_set_excl(ram_addr_t addr)
> +{
> +    return bitmap_test_and_clear_atomic(
> +                                ram_list.dirty_memory[DIRTY_MEMORY_EXCLUSIVE],
> +                                EXCL_BITMAP_GET_OFFSET(addr), 1);
> +}
> +
>  #endif
>  #endif


--
Alex Bennée