I think I already applied this patch.
K.
On 05/07/2010 09:01, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> This is to ensure fields shared writably with Dom0 get read only once
> for any consistency checking followed by actual calculations.
>
> I realized there was another multiple-read issue, a fix for which is
> also included (which at once simplifies __insert_record()).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>
> --- a/xen/common/trace.c 2010-07-01 10:05:54.000000000 +0200
> +++ b/xen/common/trace.c 2010-07-01 14:01:47.000000000 +0200
> @@ -437,11 +437,13 @@ static inline bool_t bogus(u32 prod, u32
> static inline u32 calc_unconsumed_bytes(const struct t_buf *buf)
> {
> u32 prod = buf->prod, cons = buf->cons;
> - s32 x = prod - cons;
> + s32 x;
>
> + barrier(); /* must read buf->prod and buf->cons only once */
> if ( bogus(prod, cons) )
> return data_size;
>
> + x = prod - cons;
> if ( x < 0 )
> x += 2*data_size;
>
> @@ -453,12 +455,14 @@ static inline u32 calc_unconsumed_bytes(
>
> static inline u32 calc_bytes_to_wrap(const struct t_buf *buf)
> {
> - u32 prod = buf->prod;
> - s32 x = data_size - prod;
> + u32 prod = buf->prod, cons = buf->cons;
> + s32 x;
>
> - if ( bogus(prod, buf->cons) )
> + barrier(); /* must read buf->prod and buf->cons only once */
> + if ( bogus(prod, cons) )
> return 0;
>
> + x = data_size - prod;
> if ( x <= 0 )
> x += data_size;
>
> @@ -473,11 +477,14 @@ static inline u32 calc_bytes_avail(const
> return data_size - calc_unconsumed_bytes(buf);
> }
>
> -static inline struct t_rec *next_record(const struct t_buf *buf)
> +static inline struct t_rec *next_record(const struct t_buf *buf,
> + uint32_t *next)
> {
> - u32 x = buf->prod;
> + u32 x = buf->prod, cons = buf->cons;
>
> - if ( !tb_init_done || bogus(x, buf->cons) )
> + barrier(); /* must read buf->prod and buf->cons only once */
> + *next = x;
> + if ( !tb_init_done || bogus(x, cons) )
> return NULL;
>
> if ( x >= data_size )
> @@ -504,23 +511,21 @@ static inline void __insert_record(volat
> BUG_ON(local_rec_size != rec_size);
> BUG_ON(extra & 3);
>
> + rec = next_record(buf, &next);
> + if ( !rec )
> + return;
> /* Double-check once more that we have enough space.
> * Don't bugcheck here, in case the userland tool is doing
> * something stupid. */
> - next = calc_bytes_avail(buf);
> - if ( next < rec_size )
> + if ( (unsigned char *)rec + rec_size > this_cpu(t_data) + data_size )
> {
> if ( printk_ratelimit() )
> printk(XENLOG_WARNING
> - "%s: avail=%u (size=%08x prod=%08x cons=%08x) rec=%u\n",
> - __func__, next, data_size, buf->prod, buf->cons,
> rec_size);
> + "%s: size=%08x prod=%08x cons=%08x rec=%u\n",
> + __func__, data_size, next, buf->cons, rec_size);
> return;
> }
> - rmb();
>
> - rec = next_record(buf);
> - if ( !rec )
> - return;
> rec->event = event;
> rec->extra_u32 = extra_word;
> dst = (unsigned char *)rec->u.nocycles.extra_u32;
> @@ -537,9 +542,6 @@ static inline void __insert_record(volat
>
> wmb();
>
> - next = buf->prod;
> - if ( bogus(next, buf->cons) )
> - return;
> next += rec_size;
> if ( next >= 2*data_size )
> next -= 2*data_size;
>
>
>
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