[RFC PATCH 08/28] arm64: RME: Keep a spare page delegated to the RMM

[Steven Price]

Pages can only be populated/destroyed on the RMM at the 4KB granule,
this requires creating the full depth of RTTs. However if the pages are
going to be combined into a 4MB huge page the last RTT is only
temporarily needed. Similarly when freeing memory the huge page must be
temporarily split requiring temporary usage of the full depth oF RTTs.

To avoid needing to perform a temporary allocation and delegation of a
page for this purpose we keep a spare delegated page around. In
particular this avoids the need for memory allocation while destroying
the realm guest.

Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
 arch/arm64/include/asm/kvm_rme.h | 3 +++
 arch/arm64/kvm/rme.c             | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
index 055a22accc08..a6318af3ed11 100644
--- a/arch/arm64/include/asm/kvm_rme.h
+++ b/arch/arm64/include/asm/kvm_rme.h
@@ -21,6 +21,9 @@ struct realm {
 	void *rd;
 	struct realm_params *params;
 
+	/* A spare already delegated page */
+	phys_addr_t spare_page;
+
 	unsigned long num_aux;
 	unsigned int vmid;
 	unsigned int ia_bits;
diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
index 9f8c5a91b8fc..0c9d70e4d9e6 100644
--- a/arch/arm64/kvm/rme.c
+++ b/arch/arm64/kvm/rme.c
@@ -148,6 +148,7 @@ static int realm_create_rd(struct kvm *kvm)
 	}
 
 	realm->rd = rd;
+	realm->spare_page = PHYS_ADDR_MAX;
 	realm->ia_bits = VTCR_EL2_IPA(kvm->arch.vtcr);
 
 	if (WARN_ON(rmi_rec_aux_count(rd_phys, &realm->num_aux))) {
@@ -357,6 +358,11 @@ void kvm_destroy_realm(struct kvm *kvm)
 		free_page((unsigned long)realm->rd);
 		realm->rd = NULL;
 	}
+	if (realm->spare_page != PHYS_ADDR_MAX) {
+		if (!WARN_ON(rmi_granule_undelegate(realm->spare_page)))
+			free_page((unsigned long)phys_to_virt(realm->spare_page));
+		realm->spare_page = PHYS_ADDR_MAX;
+	}
 
 	pgd_sz = kvm_pgd_pages(pgt->ia_bits, pgt->start_level);
 	for (i = 0; i < pgd_sz; i++) {
-- 
2.34.1