Re: [PATCH] kvm/x86: enlarge number of possible CPUID leaves

[Avi Kivity <avi@redhat.com>]

On 12/01/2010 01:17 PM, Andre Przywara wrote:
> Currently the number of CPUID leaves KVM handles is limited to 40.
> My desktop machine (AthlonII) already has 35 and future CPUs will
> expand this well beyond the limit. Extend the limit to 80 to make
> room for future processors.
>
> Signed-off-by: Andre Przywara<andre.przywara@amd.com>
> ---
>   arch/x86/include/asm/kvm_host.h |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> Hi,
> I found that either KVM or QEMU (possibly both) are broken in respect
> to handling more CPUID entries than the limit dictates. KVM will
> return -E2BIG, which is the same error as if the user hasn't provided
> enough space to hold all entries. Now QEMU will continue to enlarge
> the allocated memory until it gets into an out-of-memory condition.
> I have tried to fix this with teaching KVM how to deal with a capped
> number of entries (there are some bugs in the current code), but this
> will limit the number of CPUID entries KVM handles, which will surely
> cut of the lastly appended PV leaves.
> A proper fix would be to make this allocation dynamic. Is this a
> feasible way or will this lead to issues or side-effects?
>

Well, there has to be some limit, or userspace can allocate unbounded 
kernel memory.

-- 
error compiling committee.c: too many arguments to function