[RFC PATCH 41/45] KVM: arm64: pkvm: Add __pkvm_host_add_remove_page()

[Jean-Philippe Brucker]

Add a small helper to remove and add back a page from the host stage-2.
This will be used to temporarily unmap a piece of shared sram (device
memory) from the host while we handle a SCMI request, preventing the
host from modifying the request after it is verified.

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  1 +
 arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index a363d58a998b..a7b28307604d 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -75,6 +75,7 @@ int __pkvm_guest_share_host(struct pkvm_hyp_vcpu *hyp_vcpu, u64 ipa);
 int __pkvm_guest_unshare_host(struct pkvm_hyp_vcpu *hyp_vcpu, u64 ipa);
 int __pkvm_host_share_dma(u64 phys_addr, size_t size, bool is_ram);
 int __pkvm_host_unshare_dma(u64 phys_addr, size_t size);
+int __pkvm_host_add_remove_page(u64 pfn, bool remove);
 
 bool addr_is_memory(phys_addr_t phys);
 int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index dcf08ce03790..6c3eeea4d4f5 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -1954,3 +1954,20 @@ int __pkvm_host_reclaim_page(u64 pfn)
 
 	return ret;
 }
+
+/*
+ * Temporarily unmap a page from the host stage-2, if @remove is true, or put it
+ * back. After restoring the ownership to host, the page will be lazy-mapped.
+ */
+int __pkvm_host_add_remove_page(u64 pfn, bool remove)
+{
+	int ret;
+	u64 host_addr = hyp_pfn_to_phys(pfn);
+	u8 owner = remove ? PKVM_ID_HYP : PKVM_ID_HOST;
+
+	host_lock_component();
+	ret = host_stage2_set_owner_locked(host_addr, PAGE_SIZE, owner);
+	host_unlock_component();
+
+	return ret;
+}
-- 
2.39.0