Re: [PATCH 6/6] KVM: Move flags check for user memory regions to the ioctl() specific API

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 8/3/2024 4:50 AM, Sean Christopherson wrote:
> Move the check on memory region flags to kvm_vm_ioctl_set_memory_region()
> now that the internal API, kvm_set_internal_memslot(), disallows any and
> all flags.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   virt/kvm/kvm_main.c | 54 ++++++++++++++++++---------------------------
>   1 file changed, 22 insertions(+), 32 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 84fcb20e3e1c..09cc261b080a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1566,34 +1566,6 @@ static void kvm_replace_memslot(struct kvm *kvm,
>   #define KVM_SET_USER_MEMORY_REGION_V1_FLAGS \
>   	(KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_READONLY)
>   
> -static int check_memory_region_flags(struct kvm *kvm,
> -				     const struct kvm_userspace_memory_region2 *mem)
> -{
> -	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> -
> -	if (kvm_arch_has_private_mem(kvm))
> -		valid_flags |= KVM_MEM_GUEST_MEMFD;
> -
> -	/* Dirty logging private memory is not currently supported. */
> -	if (mem->flags & KVM_MEM_GUEST_MEMFD)
> -		valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
> -
> -#ifdef CONFIG_HAVE_KVM_READONLY_MEM
> -	/*
> -	 * GUEST_MEMFD is incompatible with read-only memslots, as writes to
> -	 * read-only memslots have emulated MMIO, not page fault, semantics,
> -	 * and KVM doesn't allow emulated MMIO for private memory.
> -	 */
> -	if (!(mem->flags & KVM_MEM_GUEST_MEMFD))
> -		valid_flags |= KVM_MEM_READONLY;
> -#endif
> -
> -	if (mem->flags & ~valid_flags)
> -		return -EINVAL;
> -
> -	return 0;
> -}

I would vote for keeping it instead of open coding it.

> -
>   static void kvm_swap_active_memslots(struct kvm *kvm, int as_id)
>   {
>   	struct kvm_memslots *slots = kvm_get_inactive_memslots(kvm, as_id);
> @@ -1986,10 +1958,6 @@ static int kvm_set_memory_region(struct kvm *kvm,
>   
>   	lockdep_assert_held(&kvm->slots_lock);
>   
> -	r = check_memory_region_flags(kvm, mem);
> -	if (r)
> -		return r;
> -
>   	as_id = mem->slot >> 16;
>   	id = (u16)mem->slot;
>   
> @@ -2114,6 +2082,28 @@ EXPORT_SYMBOL_GPL(kvm_set_internal_memslot);
>   static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
>   					  struct kvm_userspace_memory_region2 *mem)
>   {
> +	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> +
> +	if (kvm_arch_has_private_mem(kvm))
> +		valid_flags |= KVM_MEM_GUEST_MEMFD;
> +
> +	/* Dirty logging private memory is not currently supported. */
> +	if (mem->flags & KVM_MEM_GUEST_MEMFD)
> +		valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
> +
> +#ifdef CONFIG_HAVE_KVM_READONLY_MEM
> +	/*
> +	 * GUEST_MEMFD is incompatible with read-only memslots, as writes to
> +	 * read-only memslots have emulated MMIO, not page fault, semantics,
> +	 * and KVM doesn't allow emulated MMIO for private memory.
> +	 */
> +	if (!(mem->flags & KVM_MEM_GUEST_MEMFD))
> +		valid_flags |= KVM_MEM_READONLY;
> +#endif
> +
> +	if (mem->flags & ~valid_flags)
> +		return -EINVAL;
> +
>   	if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
>   		return -EINVAL;
>