KVM: arm64: Prepare the creation of s1 mappings at EL2

When memory protection is enabled, the EL2 code needs the ability to
create and manage its own page-table. To do so, introduce a new set of
hypercalls to bootstrap a memory management system at EL2.

This leads to the following boot flow in nVHE Protected mode:

 1. the host allocates memory for the hypervisor very early on, using
    the memblock API;

 2. the host creates a set of stage 1 page-table for EL2, installs the
    EL2 vectors, and issues the __pkvm_init hypercall;

 3. during __pkvm_init, the hypervisor re-creates its stage 1 page-table
    and stores it in the memory pool provided by the host;

 4. the hypervisor then extends its stage 1 mappings to include a
    vmemmap in the EL2 VA space, hence allowing to use the buddy
    allocator introduced in a previous patch;

 5. the hypervisor jumps back in the idmap page, switches from the
    host-provided page-table to the new one, and wraps up its
    initialization by enabling the new allocator, before returning to
    the host.

 6. the host can free the now unused page-table created for EL2, and
    will now need to issue hypercalls to make changes to the EL2 stage 1
    mappings instead of modifying them directly.

Note that for the sake of simplifying the review, this patch focuses on
the hypervisor side of things. In other words, this only implements the
new hypercalls, but does not make use of them from the host yet. The
host-side changes will follow in a subsequent patch.

Credits to Will for __pkvm_init_switch_pgd.

Acked-by: Will Deacon <will@kernel.org>
Co-authored-by: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-18-qperret@google.com

1 files changed, 27 insertions, 0 deletions

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
index c631e29fb001..a2b8b6a84cbd 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S
@@ -244,4 +244,31 @@ alternative_else_nop_endif
 
 SYM_CODE_END(__kvm_handle_stub_hvc)
 
+SYM_FUNC_START(__pkvm_init_switch_pgd)
+	/* Turn the MMU off */
+	pre_disable_mmu_workaround
+	mrs	x2, sctlr_el2
+	bic	x3, x2, #SCTLR_ELx_M
+	msr	sctlr_el2, x3
+	isb
+
+	tlbi	alle2
+
+	/* Install the new pgtables */
+	ldr	x3, [x0, #NVHE_INIT_PGD_PA]
+	phys_to_ttbr x4, x3
+alternative_if ARM64_HAS_CNP
+	orr	x4, x4, #TTBR_CNP_BIT
+alternative_else_nop_endif
+	msr	ttbr0_el2, x4
+
+	/* Set the new stack pointer */
+	ldr	x0, [x0, #NVHE_INIT_STACK_HYP_VA]
+	mov	sp, x0
+
+	/* And turn the MMU back on! */
+	set_sctlr_el2	x2
+	ret	x1
+SYM_FUNC_END(__pkvm_init_switch_pgd)
+
 	.popsection