[Qemu-devel] Re: [PATCH] kvm: Fix overlapping check for memory slots

[Sheng Yang <sheng@linux.intel.com>]

On Monday 13 April 2009 16:50:40 Jan Kiszka wrote:
> Sheng Yang wrote:
> > On Saturday 11 April 2009 17:48:04 Jan Kiszka wrote:
> >> This nice little buglet complicates a smarter slot management in qemu
> >> user space just "slightly". Sigh...
> >>
> >> -------->
> >>
> >> When checking for overlapping slots on registration of a new one, kvm
> >> currently also considers zero-length (ie. deleted) slots and rejects
> >> requests incorrectly. This finally denies user space from joining slots.
> >> Fix the check by skipping deleted slots.
> >>
> >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >> ---
> >>
> >>  virt/kvm/kvm_main.c |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >> index 363af32..18f06d2 100644
> >> --- a/virt/kvm/kvm_main.c
> >> +++ b/virt/kvm/kvm_main.c
> >> @@ -1117,7 +1117,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >>  	for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
> >>  		struct kvm_memory_slot *s = &kvm->memslots[i];
> >>
> >> -		if (s == memslot)
> >> +		if (s == memslot || !s->npages)
> >>  			continue;
> >>  		if (!((base_gfn + npages <= s->base_gfn) ||
> >>  		      (base_gfn >= s->base_gfn + s->npages)))
> >
> > Is it necessary to preserve a valid base_gfn/flags/etc for a zeroed slot?
> > Seems kvm_free_physmem_slot didn't clean them.
>
> It is not necessary as long as we ignore such slots (as this patch does).

What I think is, if they are invalid and unnecessary to keep, it's better to 
clean them rather than add a additional check, for it should covered by 
current check. 

-- 
regards
Yang, Sheng