KVM: arm64: Add kimg_hyp_va() helper

KVM/arm64 is so far unable to deal with function pointers, as the compiler
will generate the kernel's runtime VA, and not the linear mapping address,
meaning that kern_hyp_va() will give the wrong result.

We so far have been able to use PC-relative addressing, but that's not
always easy to use, and prevents the implementation of things like
the mapping of an index to a pointer.

To allow this, provide a new helper that computes the required
translation from the kernel image to the HYP VA space.

Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_mmu.h

@@ -98,6 +98,24 @@ static __always_inline unsigned long __kern_hyp_va(unsigned long v)
 
 #define kern_hyp_va(v) 	((typeof(v))(__kern_hyp_va((unsigned long)(v))))
 
+static __always_inline unsigned long __kimg_hyp_va(unsigned long v)
+{
+	unsigned long offset;
+
+	asm volatile(ALTERNATIVE_CB("movz %0, #0\n"
+				    "movk %0, #0, lsl #16\n"
+				    "movk %0, #0, lsl #32\n"
+				    "movk %0, #0, lsl #48\n",
+				    kvm_update_kimg_phys_offset)
+		     : "=r" (offset));
+
+	return __kern_hyp_va((v - offset) | PAGE_OFFSET);
+}
+
+#define kimg_fn_hyp_va(v) 	((typeof(*v))(__kimg_hyp_va((unsigned long)(v))))
+
+#define kimg_fn_ptr(x)	(typeof(x) **)(x)
+
 /*
  * We currently support using a VM-specified IPA size. For backward
  * compatibility, the default IPA size is fixed to 40bits.

arch/arm64/kvm/va_layout.c

@@ -11,6 +11,7 @@
 #include <asm/debug-monitors.h>
 #include <asm/insn.h>
 #include <asm/kvm_mmu.h>
+#include <asm/memory.h>
 
 /*
  * The LSB of the HYP VA tag
@@ -201,3 +202,52 @@ void kvm_patch_vector_branch(struct alt_instr *alt,
 					   AARCH64_INSN_BRANCH_NOLINK);
 	*updptr++ = cpu_to_le32(insn);
 }
+
+static void generate_mov_q(u64 val, __le32 *origptr, __le32 *updptr, int nr_inst)
+{
+	u32 insn, oinsn, rd;
+
+	BUG_ON(nr_inst != 4);
+
+	/* Compute target register */
+	oinsn = le32_to_cpu(*origptr);
+	rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, oinsn);
+
+	/* movz rd, #(val & 0xffff) */
+	insn = aarch64_insn_gen_movewide(rd,
+					 (u16)val,
+					 0,
+					 AARCH64_INSN_VARIANT_64BIT,
+					 AARCH64_INSN_MOVEWIDE_ZERO);
+	*updptr++ = cpu_to_le32(insn);
+
+	/* movk rd, #((val >> 16) & 0xffff), lsl #16 */
+	insn = aarch64_insn_gen_movewide(rd,
+					 (u16)(val >> 16),
+					 16,
+					 AARCH64_INSN_VARIANT_64BIT,
+					 AARCH64_INSN_MOVEWIDE_KEEP);
+	*updptr++ = cpu_to_le32(insn);
+
+	/* movk rd, #((val >> 32) & 0xffff), lsl #32 */
+	insn = aarch64_insn_gen_movewide(rd,
+					 (u16)(val >> 32),
+					 32,
+					 AARCH64_INSN_VARIANT_64BIT,
+					 AARCH64_INSN_MOVEWIDE_KEEP);
+	*updptr++ = cpu_to_le32(insn);
+
+	/* movk rd, #((val >> 48) & 0xffff), lsl #48 */
+	insn = aarch64_insn_gen_movewide(rd,
+					 (u16)(val >> 48),
+					 48,
+					 AARCH64_INSN_VARIANT_64BIT,
+					 AARCH64_INSN_MOVEWIDE_KEEP);
+	*updptr++ = cpu_to_le32(insn);
+}
+
+void kvm_update_kimg_phys_offset(struct alt_instr *alt,
+				 __le32 *origptr, __le32 *updptr, int nr_inst)
+{
+	generate_mov_q(kimage_voffset + PHYS_OFFSET, origptr, updptr, nr_inst);
+}