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xenfb.c: avoid expensive loops when prod <= out_cons

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If the frontend sets out_cons to a value higher than out_prod, it will
cause xenfb_handle_events to loop about 2^32 times. Avoid that by using
better checks at the beginning of the function.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reported-by: Ling Liu <liuling-it@360.cn>
This commit is contained in:
Stefano Stabellini 2016-01-06 16:32:22 +00:00
parent 9027ac50fd
commit ac0487e1d2
1 changed files with 3 additions and 2 deletions
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5
hw/display/xenfb.c
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@ -789,8 +789,9 @@ static void xenfb_handle_events(struct XenFB *xenfb)
prod = page->out_prod; prod = page->out_prod;
out_cons = page->out_cons; out_cons = page->out_cons;
if (prod == out_cons) if (prod - out_cons >= XENFB_OUT_RING_LEN) {
return; return;
}
xen_rmb(); /* ensure we see ring contents up to prod */ xen_rmb(); /* ensure we see ring contents up to prod */
for (cons = out_cons; cons != prod; cons++) { for (cons = out_cons; cons != prod; cons++) {
union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons); union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons);