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SubjectRe: [PATCH v5 04/13] KVM: x86: Move n_memslots_pages recalc to kvm_arch_prepare_memory_region()
Date
On 20.10.2021 00:38, Sean Christopherson wrote:
> On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:
>> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>>
>> This allows us to return a proper error code in case we spot an underflow.
>>
>> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
>> ---
>> arch/x86/kvm/x86.c | 49 ++++++++++++++++++++++++++--------------------
>> 1 file changed, 28 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 97d86223427d..0fffb8414009 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -11511,9 +11511,23 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>> const struct kvm_userspace_memory_region *mem,
>> enum kvm_mr_change change)
>> {
>> - if (change == KVM_MR_CREATE || change == KVM_MR_MOVE)
>> - return kvm_alloc_memslot_metadata(kvm, new,
>> - mem->memory_size >> PAGE_SHIFT);
>> + if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) {
>> + int ret;
>> +
>> + ret = kvm_alloc_memslot_metadata(kvm, new,
>> + mem->memory_size >> PAGE_SHIFT);
>> + if (ret)
>> + return ret;
>> +
>> + if (change == KVM_MR_CREATE)
>> + kvm->arch.n_memslots_pages += new->npages;
>> + } else if (change == KVM_MR_DELETE) {
>> + if (WARN_ON(kvm->arch.n_memslots_pages < old->npages))
>> + return -EIO;
>
> This is not worth the churn. In a way, it's worse because userspace can spam
> the living snot out of the kernel log by retrying the ioctl().
>
> Since underflow can happen if and only if there's a KVM bug, and a pretty bad one
> at that, just make the original WARN_ON a KVM_BUG_ON. That will kill the VM and
> also provide the WARN_ON_ONCE behavior that we probably want.

Will do.

Thanks,
Maciej

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