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From: Hugh Dickins <hugh@veritas.com> Date: Fri, 18 Nov 2005 08:13:54 +0000 (GMT) > On Fri, 18 Nov 2005, David S. Miller wrote: > > From: Hugh Dickins <hugh@veritas.com> > > Date: Fri, 18 Nov 2005 08:02:02 +0000 (GMT) > > > > > That code is necessary to reproduce the existing behaviour, which has > > > always done COW on PageReserved mappings without complaint - if the > > > vm_page_prot didn't already let you slip through without a WP fault. > > > > And there is evidence today that this is really needed, at least > > by vbetool. > > > > Ok, we need COW on VM_UNPAGED. :) > > Are you so sure of that, that we should even skip adding a warning? Yes, I'm pretty sure. The datapoints are like this: 1) Existing vbetool with 2.6.14 and previous works 2) 2.6.15 w/no-COW-on-reserved makes existing vbetool fail immediately (of course) 3) 2.6.15 w/no-COW-on-reserved still fails with MAP_SHARED patched vbetool 4) 2.6.15 w/COW-on-VM_UNPAGED works with existing vbetool 5) 2.6.15 w/COW-on-VM_UNPAGED _FAILS_ with MAP_SHARED patched vbetool That #5 is the key. If we use MAP_SHARED and let vbetool modify the real BIOS data area, resume fails. That's convincing enough for me :) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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