Hi Quentin,

On Tue, Nov 17, 2020 at 06:15:56PM +0000, Quentin Perret wrote:

When memory protection is enabled, the Hyp code needs the ability to
create and manage its own page-table. To do so, introduce a new set of
hypercalls to initialize Hyp memory protection.

During the init hcall, the hypervisor runs with the host-provided
page-table and uses the trivial early page allocator to create its own
set of page-tables, using a memory pool that was donated by the host.
Specifically, the hypervisor creates its own mappings for __hyp_text,
the Hyp memory pool, the __hyp_bss, the portion of hyp_vmemmap
corresponding to the Hyp pool, among other things. It then jumps back in
the idmap page, switches to use the newly-created pgd (instead of the
temporary one provided by the host) and then installs the full-fledged
buddy allocator which will then be the only one in used from then on.

Note that for the sake of symplifying the review, this only introduces
the code doing this operation, without actually being called by anyhing
yet. This will be done in a subsequent patch, which will introduce the
necessary host kernel changes.

[...]

[...]

+extern bool enable_protected_kvm;
+void __init reserve_kvm_hyp(void)
+{
+	u64 nr_pages, prev;
+
+	if (!enable_protected_kvm)
+		return;
+
+	if (!is_hyp_mode_available() || is_kernel_in_hyp_mode())
+		return;
+
+	if (kvm_nvhe_sym(hyp_memblock_nr) <= 0)
+		return;
+
+	hyp_mem_size += num_possible_cpus() << PAGE_SHIFT;
+	hyp_mem_size += hyp_s1_pgtable_size();
+
+	/*
+	 * The hyp_vmemmap needs to be backed by pages, but these pages
+	 * themselves need to be present in the vmemmap, so compute the number
+	 * of pages needed by looking for a fixed point.
+	 */
+	nr_pages = 0;
+	do {
+		prev = nr_pages;
+		nr_pages = (hyp_mem_size >> PAGE_SHIFT) + prev;
+		nr_pages = DIV_ROUND_UP(nr_pages * sizeof(struct hyp_page), PAGE_SIZE);
+		nr_pages += __hyp_pgtable_max_pages(nr_pages);
+	} while (nr_pages != prev);
+	hyp_mem_size += nr_pages << PAGE_SHIFT;
+
+	hyp_mem_base = memblock_find_in_range(0, memblock_end_of_DRAM(),
+					      hyp_mem_size, SZ_2M);
+	if (!hyp_mem_base) {
+		kvm_err("Failed to reserve hyp memory\n");
+		return;
+	}
+	memblock_reserve(hyp_mem_base, hyp_mem_size);

Why not use the RESERVEDMEM_OF_DECLARE() interface for the hypervisor
memory? That way, the hypervisor memory can either be statically partitioned
as a carveout or allocated dynamically for us -- we wouldn't need to care.

Will

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