[PATCH v2 10/35] KVM: arm64: Ignore -EAGAIN when mapping in pages for the pKVM host

Will Deacon
2026-01-19T12:47:24Z

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.

Signed-off-by: Will Deacon <will@kernel.org>
---
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 49db32f3ddf7..0abf6c3acdf7 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -459,8 +459,15 @@ 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);
}

/*
@@ -502,7 +509,7 @@ 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) &&
@@ -607,7 +614,6 @@ 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)) {
@@ -626,8 +632,13 @@ 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 {
--
2.52.0.457.g6b5491de43-goog