Subject: [PATCH v4 10/38] KVM: arm64: Ignore -EAGAIN when mapping in pages for the pKVM host

From: Will Deacon <[email-masked]>
Date: Fri, 27 Mar 2026 14:00:09 +0000

If the host takes a stage-2 translation fault on two CPUs at the same
time, one of them will get back -EAGAIN from the page-table mapping code
when it runs into the mapping installed by the other.

Rather than handle this explicitly in handle_host_mem_abort(), pass the
new KVM_PGTABLE_WALK_IGNORE_EAGAIN flag to kvm_pgtable_stage2_map() from
__host_stage2_idmap() and return -EEXIST if host_stage2_adjust_range()
finds a valid pte. This will avoid having to test for -EAGAIN on the
reclaim path in subsequent patches.

Reviewed-by: Fuad Tabba <[email-masked]>
Tested-by: Fuad Tabba <[email-masked]>
Tested-by: Mostafa Saleh <[email-masked]>
Signed-off-by: Will Deacon <[email-masked]>
---
 arch/arm64/kvm/hyp/nvhe/mem_protect.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index d815265bd374..7d22893ab1dc 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -461,8 +461,15 @@ static bool range_is_memory(u64 start, u64 end)
 static inline int __host_stage2_idmap(u64 start, u64 end,
 				      enum kvm_pgtable_prot prot)
 {
+	/*
+	 * We don't make permission changes to the host idmap after
+	 * initialisation, so we can squash -EAGAIN to save callers
+	 * having to treat it like success in the case that they try to
+	 * map something that is already mapped.
+	 */
 	return kvm_pgtable_stage2_map(&host_mmu.pgt, start, end - start, start,
-				      prot, &host_s2_pool, 0);
+				      prot, &host_s2_pool,
+				      KVM_PGTABLE_WALK_IGNORE_EAGAIN);
 }
 
 /*
@@ -504,7 +511,7 @@ static int host_stage2_adjust_range(u64 addr, struct kvm_mem_range *range)
 		return ret;
 
 	if (kvm_pte_valid(pte))
-		return -EAGAIN;
+		return -EEXIST;
 
 	if (pte) {
 		WARN_ON(addr_is_memory(addr) &&
@@ -609,7 +616,6 @@ void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 {
 	struct kvm_vcpu_fault_info fault;
 	u64 esr, addr;
-	int ret = 0;
 
 	esr = read_sysreg_el2(SYS_ESR);
 	if (!__get_fault_info(esr, &fault)) {
@@ -628,8 +634,13 @@ void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 	BUG_ON(!(fault.hpfar_el2 & HPFAR_EL2_NS));
 	addr = FIELD_GET(HPFAR_EL2_FIPA, fault.hpfar_el2) << 12;
 
-	ret = host_stage2_idmap(addr);
-	BUG_ON(ret && ret != -EAGAIN);
+	switch (host_stage2_idmap(addr)) {
+	case -EEXIST:
+	case 0:
+		break;
+	default:
+		BUG();
+	}
 }
 
 struct check_walk_data {
-- 
2.53.0.1018.g2bb0e51243-goog