Re: [PATCH 3/8] KVM: arm64: Propagate and use kvm_s2_fault_result on S2 fault

On Thu, Sep 10, 2026 at 09:49:08AM +0100, Marc Zyngier wrote:

On Tue, 25 Aug 2026 17:00:37 +0100,
"Lorenzo Stoakes (ARM)" [off-list ref] wrote:

quoted

 arch/arm64/kvm/mmu.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 80cb520e25b9..da15da4e40e6 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c

@@ -1607,6 +1607,11 @@ struct kvm_s2_fault_desc {
 	struct kvm_s2_mmu	*mmu;
 };

+struct kvm_s2_fault_result {
+	unsigned long mapping_size;
+	bool mapped;
+};
+
 static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
 {
 	return esr_fsc_is_permission_fault(s2fd->esr);

@@ -1632,7 +1637,17 @@ static u64 kvm_s2_perm_fault_granule(const struct kvm_s2_fault_desc *s2fd)
 	return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(level));
 }

-static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
+static void populate_fault_result(struct kvm_s2_fault_result *result,
+				  unsigned long mapping_size)
+{
+	/* A THP upgrade may have altered mapping size. */
+	result->mapping_size = mapping_size;
+	/* -EAGAIN is swallowed so be explicit when we actually map. */
+	result->mapped = true;

I'm not sold on this boolean. I'd rather we use the fact that the
fault handler has passed a result pointer to return -EAGAIN rather
than turning into a 0, because that's a clear sign that the fault
hasn't been generated by a vcpu.

Yeah I did actually think that myself when writing it :) I was a bit in two
minds about how to do this, but yeah that's just a better way, will fix
that!

	M.

--
Without deviation from the norm, progress is not possible.

--
Cheers, Lorenzo