On Wed, Jun 18, 2025 at 01:33:17PM -0700, Sean Christopherson wrote:

On Wed, Jun 18, 2025, Oliver Upton wrote:

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Signed-off-by: Sean Christopherson <seanjc@google.com>

No need for my SoB.

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+#ifdef CONFIG_KVM_GENERIC_PAGE_FAULT
+bool kvm_do_userfault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)

The polarity of the return here feels weird. If we want a value of 0 to
indicate success then int is a better return type.

The boolean is my fault/suggestion.  My thinking is that it would make the callers
more intuitive, e.g. so that this reads "if do userfault, then exit to userspace
with -EFAULT".

	if (kvm_do_userfault(vcpu, fault))
		return -EFAULT;

Agreed, this reads correctly. My only issue is that when I read the
function signature, "bool" is usually wired the other way around.

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+{
+	struct kvm_memory_slot *slot = fault->slot;
+	unsigned long __user *user_chunk;
+	unsigned long chunk;
+	gfn_t offset;
+
+	if (!kvm_is_userfault_memslot(slot))
+		return false;
+
+	offset = fault->gfn - slot->base_gfn;
+	user_chunk = slot->userfault_bitmap + (offset / BITS_PER_LONG);
+
+	if (__get_user(chunk, user_chunk))
+		return true;

And this path is other motiviation for returning a boolean.  To me, return "success"
when a uaccess fails looks all kinds of wrong:

	if (__get_user(chunk, user_chunk))
		return 0;

Yeah, that's gross. Although I would imagine we want to express
"failure" here, game over, out to userspace for resolution. So maybe:

	if (__get_user(chunk, user_chunk))
		return -EFAULT;

That said, I don't have a super strong preference; normally I'm fanatical about
not returning booleans.  :-D

+1, it isn't _that_ big of a deal, just noticed it as part of review.

Thanks,
Oliver