[Qemu-devel] Re: [PATCH 1/5] Add target memory mapping API

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Devices accessing large amounts of memory (as with DMA) will wish to obtain
> a pointer to guest memory rather than access it indirectly via
> cpu_physical_memory_rw().  Add a new API to convert target addresses to
> host pointers.
>
> In case the target address does not correspond to RAM, a bounce buffer is
> allocated.  To prevent the guest from causing the host to allocate unbounded
> amounts of bounce buffer, this memory is limited (currently to one page).
>
> Signed-off-by: Avi Kivity <avi@redhat.com>
>   

I've gone though the thread again and I think this patch series is a 
pretty good start.  I think the API can be refined a bit more down the 
road to better support Xen but I think this is a good start.

Does anyone have major blockers with this API?  If not, I'd like to 
commit these patches.  The consumers of it should be small provided that 
we make sure to write helpers for the various types of IO pipelines.

Regards,

Anthony Liguori

> ---
>  cpu-all.h |    5 +++
>  exec.c    |   93 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 98 insertions(+), 0 deletions(-)
>
> diff --git a/cpu-all.h b/cpu-all.h
> index ee0a6e3..3439999 100644
> --- a/cpu-all.h
> +++ b/cpu-all.h
> @@ -923,6 +923,11 @@ static inline void cpu_physical_memory_write(target_phys_addr_t addr,
>  {
>      cpu_physical_memory_rw(addr, (uint8_t *)buf, len, 1);
>  }
> +void *cpu_physical_memory_map(target_phys_addr_t addr,
> +                              target_phys_addr_t *plen,
> +                              int is_write);
> +void cpu_physical_memory_unmap(void *buffer, target_phys_addr_t len,
> +                               int is_write);
>  uint32_t ldub_phys(target_phys_addr_t addr);
>  uint32_t lduw_phys(target_phys_addr_t addr);
>  uint32_t ldl_phys(target_phys_addr_t addr);
> diff --git a/exec.c b/exec.c
> index faa6333..7162271 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3045,6 +3045,99 @@ void cpu_physical_memory_write_rom(target_phys_addr_t addr,
>      }
>  }
>  
> +typedef struct {
> +    void *buffer;
> +    target_phys_addr_t addr;
> +    target_phys_addr_t len;
> +} BounceBuffer;
> +
> +static BounceBuffer bounce;
> +
> +void *cpu_physical_memory_map(target_phys_addr_t addr,
> +                              target_phys_addr_t *plen,
> +                              int is_write)
> +{
> +    target_phys_addr_t len = *plen;
> +    target_phys_addr_t done = 0;
> +    int l;
> +    uint8_t *ret = NULL;
> +    uint8_t *ptr;
> +    target_phys_addr_t page;
> +    unsigned long pd;
> +    PhysPageDesc *p;
> +    unsigned long addr1;
> +
> +    while (len > 0) {
> +        page = addr & TARGET_PAGE_MASK;
> +        l = (page + TARGET_PAGE_SIZE) - addr;
> +        if (l > len)
> +            l = len;
> +        p = phys_page_find(page >> TARGET_PAGE_BITS);
> +        if (!p) {
> +            pd = IO_MEM_UNASSIGNED;
> +        } else {
> +            pd = p->phys_offset;
> +        }
> +
> +        if ((pd & ~TARGET_PAGE_MASK) != IO_MEM_RAM) {
> +            if (done || bounce.buffer) {
> +                break;
> +            }
> +            bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE);
> +            bounce.addr = addr;
> +            bounce.len = l;
> +            if (!is_write) {
> +                cpu_physical_memory_rw(addr, bounce.buffer, l, 0);
> +            }
> +            ptr = bounce.buffer;
> +        } else {
> +            addr1 = (pd & TARGET_PAGE_MASK) + (addr & ~TARGET_PAGE_MASK);
> +            ptr = phys_ram_base + addr1;
> +        }
> +        if (!done) {
> +            ret = ptr;
> +        } else if (ret + done != ptr) {
> +            break;
> +        }
> +
> +        len -= l;
> +        addr += l;
> +        done += l;
> +    }
> +    *plen = done;
> +    return ret;
> +}
> +
> +void cpu_physical_memory_unmap(void *buffer, target_phys_addr_t len,
> +                               int is_write)
> +{
> +    if (buffer != bounce.buffer) {
> +        if (is_write) {
> +            unsigned long addr1 = (uint8_t *)buffer - phys_ram_base;
> +            do {
> +                unsigned l;
> +                l = TARGET_PAGE_SIZE;
> +                if (l > len)
> +                    l = len;
> +                if (!cpu_physical_memory_is_dirty(addr1)) {
> +                    /* invalidate code */
> +                    tb_invalidate_phys_page_range(addr1, addr1 + len, 0);
> +                    /* set dirty bit */
> +                    phys_ram_dirty[addr1 >> TARGET_PAGE_BITS] |=
> +                        (0xff & ~CODE_DIRTY_FLAG);
> +                }
> +                addr1 += l;
> +                len -= l;
> +            } while (len);
> +        }
> +        return;
> +    }
> +    if (is_write) {
> +        cpu_physical_memory_write(bounce.addr, bounce.buffer, bounce.len);
> +    }
> +    qemu_free(bounce.buffer);
> +    bounce.buffer = NULL;
> +}
>  
>  /* warning: addr must be aligned */
>  uint32_t ldl_phys(target_phys_addr_t addr)
>