KVM: arm64: Back the hypervisor 'struct hyp_page' array for all memory

The EL2 'vmemmap' array in nVHE Protected mode is currently very sparse:
only memory pages owned by the hypervisor itself have a matching 'struct
hyp_page'. However, as the size of this struct has been reduced
significantly since its introduction, it appears that we can now afford
to back the vmemmap for all of memory.

Having an easily accessible 'struct hyp_page' for every physical page in
memory provides the hypervisor with a simple mechanism to store metadata
(e.g. a refcount) that wouldn't otherwise fit in the very limited number
of software bits available in the host stage-2 page-table entries. This
will be used in subsequent patches when pinning host memory pages for
use by the hypervisor at EL2.

Tested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221110190259.26861-4-will@kernel.org

1 files changed, 26 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
index 9f4ad2a8df59..8f7b8a2314bb 100644
--- a/arch/arm64/include/asm/kvm_pkvm.h
+++ b/arch/arm64/include/asm/kvm_pkvm.h
@@ -14,6 +14,32 @@
 extern struct memblock_region kvm_nvhe_sym(hyp_memory)[];
 extern unsigned int kvm_nvhe_sym(hyp_memblock_nr);
 
+static inline unsigned long
+hyp_vmemmap_memblock_size(struct memblock_region *reg, size_t vmemmap_entry_size)
+{
+	unsigned long nr_pages = reg->size >> PAGE_SHIFT;
+	unsigned long start, end;
+
+	start = (reg->base >> PAGE_SHIFT) * vmemmap_entry_size;
+	end = start + nr_pages * vmemmap_entry_size;
+	start = ALIGN_DOWN(start, PAGE_SIZE);
+	end = ALIGN(end, PAGE_SIZE);
+
+	return end - start;
+}
+
+static inline unsigned long hyp_vmemmap_pages(size_t vmemmap_entry_size)
+{
+	unsigned long res = 0, i;
+
+	for (i = 0; i < kvm_nvhe_sym(hyp_memblock_nr); i++) {
+		res += hyp_vmemmap_memblock_size(&kvm_nvhe_sym(hyp_memory)[i],
+						 vmemmap_entry_size);
+	}
+
+	return res >> PAGE_SHIFT;
+}
+
 static inline unsigned long __hyp_pgtable_max_pages(unsigned long nr_pages)
 {
 	unsigned long total = 0, i;