Re: [Xen-devel] [PATCH 0/2] QEMU/xen: simplify cpu_ioreq_pio and cpu_ioreq_move

["Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>]

> -----Original Message-----
> From: Ian Jackson [mailto:Ian.Jackson@xxxxxxxxxxxxx]
> Sent: Saturday, December 08, 2012 12:34 AM
> To: Ian Campbell
> Cc: Stefano Stabellini; Xu, Dongxiao; xen-devel@xxxxxxxxxxxxxxxxxxx;
> qemu-devel@xxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH 0/2] QEMU/xen: simplify cpu_ioreq_pio and
> cpu_ioreq_move
> 
> Ian Campbell writes ("Re: [Xen-devel] [PATCH 0/2] QEMU/xen: simplify
> cpu_ioreq_pio and cpu_ioreq_move"):
> > On Fri, 2012-12-07 at 16:14 +0000, Ian Jackson wrote:
> > > +    target_phys_addr_t offset = (target_phys_addr_t)req->size * i;
> > > +    if (req->df) addr -= offset;
> > > +    else addr -= offset;
> >
> > One of these -= should be a += I presume?
> 
> Uh, yes.
> 
> > [...]
> > > +                write_phys_req_item((target_phys_addr_t) req->data,
> req, i, &tmp);
> >
> > This seems to be the only one with this cast, why?
> 
> This is a mistake.
> 
> > write_phys_req_item takes a target_phys_addr_t so this will happen
> > regardless I think.
> 
> Indeed.
> 
> Ian.

Tested this v2 patch on my system, and it works.

Thanks,
Dongxiao


> 
> commit fd3865f8e0d867a203b4ddcb22eefa827cfaca0a
> Author: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Date:   Fri Dec 7 16:02:04 2012 +0000
> 
>     cpu_ioreq_pio, cpu_ioreq_move: introduce read_phys_req_item,
> write_phys_req_item
> 
>     The current code compare i (int) with req->count (uint32_t) in a for
>     loop, risking an infinite loop if req->count is >INT_MAX.  It also
>     does the multiplication of req->size in a too-small type, leading to
>     integer overflows.
> 
>     Turn read_physical and write_physical into two different helper
>     functions, read_phys_req_item and write_phys_req_item, that take care
>     of adding or subtracting offset depending on sign.
> 
>     This removes the formulaic multiplication to a single place where the
>     integer overflows can be dealt with by casting to wide-enough unsigned
>     types.
> 
>     Reported-By: Dongxiao Xu <dongxiao.xu@xxxxxxxxx>
>     Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
>     Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> 
>     --
>     v2: Fix sign when !!req->df.  Remove a useless cast.
> 
> diff --git a/i386-dm/helper2.c b/i386-dm/helper2.c
> index c6d049c..63a938b 100644
> --- a/i386-dm/helper2.c
> +++ b/i386-dm/helper2.c
> @@ -339,21 +339,40 @@ static void do_outp(CPUState *env, unsigned long
> addr,
>      }
>  }
> 
> -static inline void read_physical(uint64_t addr, unsigned long size, void 
> *val)
> +/*
> + * Helper functions which read/write an object from/to physical guest
> + * memory, as part of the implementation of an ioreq.
> + *
> + * Equivalent to
> + *   cpu_physical_memory_rw(addr + (req->df ? -1 : +1) * req->size * i,
> + *                          val, req->size, 0/1)
> + * except without the integer overflow problems.
> + */
> +static void rw_phys_req_item(target_phys_addr_t addr,
> +                             ioreq_t *req, uint32_t i, void *val, int rw)
>  {
> -    return cpu_physical_memory_rw((target_phys_addr_t)addr, val, size, 0);
> +    /* Do everything unsigned so overflow just results in a truncated result
> +     * and accesses to undesired parts of guest memory, which is up
> +     * to the guest */
> +    target_phys_addr_t offset = (target_phys_addr_t)req->size * i;
> +    if (req->df) addr -= offset;
> +    else addr += offset;
> +    cpu_physical_memory_rw(addr, val, req->size, rw);
>  }
> -
> -static inline void write_physical(uint64_t addr, unsigned long size, void 
> *val)
> +static inline void read_phys_req_item(target_phys_addr_t addr,
> +                                      ioreq_t *req, uint32_t i, void
> *val)
>  {
> -    return cpu_physical_memory_rw((target_phys_addr_t)addr, val, size, 1);
> +    rw_phys_req_item(addr, req, i, val, 0);
> +}
> +static inline void write_phys_req_item(target_phys_addr_t addr,
> +                                       ioreq_t *req, uint32_t i, void
> *val)
> +{
> +    rw_phys_req_item(addr, req, i, val, 1);
>  }
> 
>  static void cpu_ioreq_pio(CPUState *env, ioreq_t *req)
>  {
> -    int i, sign;
> -
> -    sign = req->df ? -1 : 1;
> +    uint32_t i;
> 
>      if (req->dir == IOREQ_READ) {
>          if (!req->data_is_ptr) {
> @@ -363,9 +382,7 @@ static void cpu_ioreq_pio(CPUState *env, ioreq_t *req)
> 
>              for (i = 0; i < req->count; i++) {
>                  tmp = do_inp(env, req->addr, req->size);
> -                write_physical((target_phys_addr_t) req->data
> -                  + (sign * i * req->size),
> -                  req->size, &tmp);
> +                write_phys_req_item(req->data, req, i, &tmp);
>              }
>          }
>      } else if (req->dir == IOREQ_WRITE) {
> @@ -375,9 +392,7 @@ static void cpu_ioreq_pio(CPUState *env, ioreq_t *req)
>              for (i = 0; i < req->count; i++) {
>                  unsigned long tmp = 0;
> 
> -                read_physical((target_phys_addr_t) req->data
> -                  + (sign * i * req->size),
> -                  req->size, &tmp);
> +                read_phys_req_item(req->data, req, i, &tmp);
>                  do_outp(env, req->addr, req->size, tmp);
>              }
>          }
> @@ -386,22 +401,16 @@ static void cpu_ioreq_pio(CPUState *env, ioreq_t
> *req)
> 
>  static void cpu_ioreq_move(CPUState *env, ioreq_t *req)
>  {
> -    int i, sign;
> -
> -    sign = req->df ? -1 : 1;
> +    uint32_t i;
> 
>      if (!req->data_is_ptr) {
>          if (req->dir == IOREQ_READ) {
>              for (i = 0; i < req->count; i++) {
> -                read_physical(req->addr
> -                  + (sign * i * req->size),
> -                  req->size, &req->data);
> +                read_phys_req_item(req->addr, req, i, &req->data);
>              }
>          } else if (req->dir == IOREQ_WRITE) {
>              for (i = 0; i < req->count; i++) {
> -                write_physical(req->addr
> -                  + (sign * i * req->size),
> -                  req->size, &req->data);
> +                write_phys_req_item(req->addr, req, i, &req->data);
>              }
>          }
>      } else {
> @@ -409,21 +418,13 @@ static void cpu_ioreq_move(CPUState *env, ioreq_t
> *req)
> 
>          if (req->dir == IOREQ_READ) {
>              for (i = 0; i < req->count; i++) {
> -                read_physical(req->addr
> -                  + (sign * i * req->size),
> -                  req->size, &tmp);
> -                write_physical((target_phys_addr_t )req->data
> -                  + (sign * i * req->size),
> -                  req->size, &tmp);
> +                read_phys_req_item(req->addr, req, i, &tmp);
> +                write_phys_req_item(req->data, req, i, &tmp);
>              }
>          } else if (req->dir == IOREQ_WRITE) {
>              for (i = 0; i < req->count; i++) {
> -                read_physical((target_phys_addr_t) req->data
> -                  + (sign * i * req->size),
> -                  req->size, &tmp);
> -                write_physical(req->addr
> -                  + (sign * i * req->size),
> -                  req->size, &tmp);
> +                read_phys_req_item(req->data, req, i, &tmp);
> +                write_phys_req_item(req->addr, req, i, &tmp);
>              }
>          }
>      }

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