Re: [PATCH v2 01/15] KVM: Do not restrict the size of KVM-internal memory regions

Christoph Schlameuss
2025-01-16T12:18:14Z

On Thu Jan 16, 2025 at 12:33 PM CET, Claudio Imbrenda wrote:
> From: Sean Christopherson <seanjc@google.com>
>
> Exempt KVM-internal memslots from the KVM_MEM_MAX_NR_PAGES restriction, as
> the limit on the number of pages exists purely to play nice with dirty
> bitmap operations, which use 32-bit values to index the bitmaps, and dirty
> logging isn't supported for KVM-internal memslots.
>
> Link: https://lore.kernel.org/all/20240802205003.353672-6-seanjc@google.com
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>

> ---
> virt/kvm/kvm_main.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a8a84bf450f9..ee3f040a4891 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1966,7 +1966,15 @@ static int kvm_set_memory_region(struct kvm *kvm,
> return -EINVAL;
> if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> return -EINVAL;
> - if ((mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
> +
> + /*
> + * The size of userspace-defined memory regions is restricted in order
> + * to play nice with dirty bitmap operations, which are indexed with an
> + * "unsigned int". KVM's internal memory regions don't support dirty
> + * logging, and so are exempt.
> + */
> + if (id < KVM_USER_MEM_SLOTS &&
> + (mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
> return -EINVAL;
>
> slots = __kvm_memslots(kvm, as_id);