Re: [Qemu-devel] [PATCH v4 41/47] qemu_ram_block_from_host

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Oct 03, 2014 at 06:47:47PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Postcopy sends RAMBlock names and offsets over the wire (since it can't
> rely on the order of ramaddr being the same), and it starts out with
> HVA fault addresses from the kernel.
> 
> qemu_ram_block_from_host translates a HVA into a RAMBlock, an offset
> in the RAMBlock, the global ram_addr_t value and it's bitmap position.

s/it's/its/

I find most of the passing around of bitmap positions confusing in
this patch series.  Would it make things simpler if you broke up the
bitmap into (aligned) per-ramblock chunks.  Then the offset would
determine the bitmap position, which is easier to understand since it
has an "inherent" meaning outside of the secondary data structure used
to track things.

> Rewrite qemu_ram_addr_from_host to use qemu_ram_block_from_host.
> 
> Provide qemu_ram_get_idstr since it's the actual name text sent on the
> wire.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  exec.c                    | 56 ++++++++++++++++++++++++++++++++++++++++++-----
>  include/exec/cpu-common.h |  4 ++++
>  2 files changed, 55 insertions(+), 5 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 65ee612..07722b3 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1246,6 +1246,11 @@ static RAMBlock *find_ram_block(ram_addr_t addr)
>      return NULL;
>  }
>  
> +const char *qemu_ram_get_idstr(RAMBlock *rb)
> +{
> +    return rb->idstr;
> +}
> +
>  void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev)
>  {
>      RAMBlock *new_block = find_ram_block(addr);
> @@ -1603,16 +1608,35 @@ static void *qemu_ram_ptr_length(ram_addr_t addr, hwaddr *size)
>      }
>  }
>  
> -/* Some of the softmmu routines need to translate from a host pointer
> -   (typically a TLB entry) back to a ram offset.  */
> -MemoryRegion *qemu_ram_addr_from_host(void *ptr, ram_addr_t *ram_addr)
> +/*
> + * Translates a host ptr back to a RAMBlock, a ram_addr and an offset
> + * in that RAMBlock.
> + *
> + * ptr: Host pointer to look up
> + * round_offset: If true round the result offset down to a page boundary
> + * *ram_addr: set to result ram_addr
> + * *offset: set to result offset within the RAMBlock
> + * *bm_index: bitmap index (i.e. scaled ram_addr for use where the scale
> + *                          isn't available)
> + *
> + * Returns: RAMBlock (or NULL if not found)
> + */
> +RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
> +                                   ram_addr_t *ram_addr,
> +                                   ram_addr_t *offset,
> +                                   unsigned long *bm_index)
>  {
>      RAMBlock *block;
>      uint8_t *host = ptr;
>  
>      if (xen_enabled()) {
>          *ram_addr = xen_ram_addr_from_mapcache(ptr);
> -        return qemu_get_ram_block(*ram_addr)->mr;
> +        block = qemu_get_ram_block(*ram_addr);
> +        if (!block) {
> +            return NULL;
> +        }
> +        *offset = (host - block->host);
> +        return block;
>      }
>  
>      block = ram_list.mru_block;
> @@ -1633,7 +1657,29 @@ MemoryRegion *qemu_ram_addr_from_host(void *ptr, ram_addr_t *ram_addr)
>      return NULL;
>  
>  found:
> -    *ram_addr = block->offset + (host - block->host);
> +    *offset = (host - block->host);
> +    if (round_offset) {
> +        *offset &= TARGET_PAGE_MASK;
> +    }

This seems clumsy.  Surely the caller can apply the mask itself it it
wants that.

> +    *ram_addr = block->offset + *offset;
> +    *bm_index = *ram_addr >> TARGET_PAGE_BITS;
> +    return block;
> +}
> +
> +/* Some of the softmmu routines need to translate from a host pointer
> +   (typically a TLB entry) back to a ram offset.  */
> +MemoryRegion *qemu_ram_addr_from_host(void *ptr, ram_addr_t *ram_addr)
> +{
> +    RAMBlock *block;
> +    ram_addr_t offset; /* Not used */
> +    unsigned long index; /* Not used */
> +
> +    block = qemu_ram_block_from_host(ptr, false, ram_addr, &offset, &index);
> +
> +    if (!block) {
> +        return NULL;
> +    }
> +
>      return block->mr;
>  }
>  
> diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
> index 8042f50..ae25407 100644
> --- a/include/exec/cpu-common.h
> +++ b/include/exec/cpu-common.h
> @@ -55,8 +55,12 @@ typedef uint32_t CPUReadMemoryFunc(void *opaque, hwaddr addr);
>  void qemu_ram_remap(ram_addr_t addr, ram_addr_t length);
>  /* This should not be used by devices.  */
>  MemoryRegion *qemu_ram_addr_from_host(void *ptr, ram_addr_t *ram_addr);
> +RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
> +                                   ram_addr_t *ram_addr, ram_addr_t *offset,
> +                                   unsigned long *bm_index);
>  void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev);
>  void qemu_ram_unset_idstr(ram_addr_t addr);
> +const char *qemu_ram_get_idstr(RAMBlock *rb);
>  
>  void cpu_physical_memory_rw(hwaddr addr, uint8_t *buf,
>                              int len, int is_write);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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