arm64: KVM: Dynamically patch the kernel/hyp VA mask

So far, we're using a complicated sequence of alternatives to
patch the kernel/hyp VA mask on non-VHE, and NOP out the
masking altogether when on VHE.

The newly introduced dynamic patching gives us the opportunity
to simplify that code by patching a single instruction with
the correct mask (instead of the mind bending cumulative masking
we have at the moment) or even a single NOP on VHE. This also
adds some initial code that will allow the patching callback
to switch to a more complex patching.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/kvm_mmu.h

@@ -69,9 +69,6 @@
  * mappings, and none of this applies in that case.
  */
 
-#define HYP_PAGE_OFFSET_HIGH_MASK	((UL(1) << VA_BITS) - 1)
-#define HYP_PAGE_OFFSET_LOW_MASK	((UL(1) << (VA_BITS - 1)) - 1)
-
 #ifdef __ASSEMBLY__
 
 #include <asm/alternative.h>
@@ -81,28 +78,15 @@
  * Convert a kernel VA into a HYP VA.
  * reg: VA to be converted.
  *
- * This generates the following sequences:
- * - High mask:
- *		and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK
- *		nop
- * - Low mask:
- *		and x0, x0, #HYP_PAGE_OFFSET_HIGH_MASK
- *		and x0, x0, #HYP_PAGE_OFFSET_LOW_MASK
- * - VHE:
- *		nop
- *		nop
- *
- * The "low mask" version works because the mask is a strict subset of
- * the "high mask", hence performing the first mask for nothing.
- * Should be completely invisible on any viable CPU.
+ * The actual code generation takes place in kvm_update_va_mask, and
+ * the instructions below are only there to reserve the space and
+ * perform the register allocation (kvm_update_va_mask uses the
+ * specific registers encoded in the instructions).
  */
 .macro kern_hyp_va	reg
-alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
-	and     \reg, \reg, #HYP_PAGE_OFFSET_HIGH_MASK
-alternative_else_nop_endif
-alternative_if ARM64_HYP_OFFSET_LOW
-	and     \reg, \reg, #HYP_PAGE_OFFSET_LOW_MASK
-alternative_else_nop_endif
+alternative_cb kvm_update_va_mask
+	and     \reg, \reg, #1
+alternative_cb_end
 .endm
 
 #else
@@ -113,18 +97,14 @@ alternative_else_nop_endif
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
 
+void kvm_update_va_mask(struct alt_instr *alt,
+			__le32 *origptr, __le32 *updptr, int nr_inst);
+
 static inline unsigned long __kern_hyp_va(unsigned long v)
 {
-	asm volatile(ALTERNATIVE("and %0, %0, %1",
-				 "nop",
-				 ARM64_HAS_VIRT_HOST_EXTN)
-		     : "+r" (v)
-		     : "i" (HYP_PAGE_OFFSET_HIGH_MASK));
-	asm volatile(ALTERNATIVE("nop",
-				 "and %0, %0, %1",
-				 ARM64_HYP_OFFSET_LOW)
-		     : "+r" (v)
-		     : "i" (HYP_PAGE_OFFSET_LOW_MASK));
+	asm volatile(ALTERNATIVE_CB("and %0, %0, #1\n",
+				    kvm_update_va_mask)
+		     : "+r" (v));
 	return v;
 }
 

arch/arm64/kvm/Makefile

@@ -16,7 +16,7 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/e
 kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arm.o $(KVM)/arm/mmu.o $(KVM)/arm/mmio.o
 kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/psci.o $(KVM)/arm/perf.o
 
-kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o
+kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o va_layout.o
 kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o
 kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o sys_regs_generic_v8.o
 kvm-$(CONFIG_KVM_ARM_HOST) += vgic-sys-reg-v3.o

arch/arm64/kvm/va_layout.c

@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2017 ARM Ltd.
+ * Author: Marc Zyngier <marc.zyngier@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/kvm_host.h>
+#include <asm/alternative.h>
+#include <asm/debug-monitors.h>
+#include <asm/insn.h>
+#include <asm/kvm_mmu.h>
+
+#define HYP_PAGE_OFFSET_HIGH_MASK	((UL(1) << VA_BITS) - 1)
+#define HYP_PAGE_OFFSET_LOW_MASK	((UL(1) << (VA_BITS - 1)) - 1)
+
+static u64 va_mask;
+
+static void compute_layout(void)
+{
+	phys_addr_t idmap_addr = __pa_symbol(__hyp_idmap_text_start);
+	unsigned long mask = HYP_PAGE_OFFSET_HIGH_MASK;
+
+	/*
+	 * Activate the lower HYP offset only if the idmap doesn't
+	 * clash with it,
+	 */
+	if (idmap_addr > HYP_PAGE_OFFSET_LOW_MASK)
+		mask = HYP_PAGE_OFFSET_LOW_MASK;
+
+	va_mask = mask;
+}
+
+static u32 compute_instruction(int n, u32 rd, u32 rn)
+{
+	u32 insn = AARCH64_BREAK_FAULT;
+
+	switch (n) {
+	case 0:
+		insn = aarch64_insn_gen_logical_immediate(AARCH64_INSN_LOGIC_AND,
+							  AARCH64_INSN_VARIANT_64BIT,
+							  rn, rd, va_mask);
+		break;
+	}
+
+	return insn;
+}
+
+void __init kvm_update_va_mask(struct alt_instr *alt,
+			       __le32 *origptr, __le32 *updptr, int nr_inst)
+{
+	int i;
+
+	/* We only expect a single instruction in the alternative sequence */
+	BUG_ON(nr_inst != 1);
+
+	if (!has_vhe() && !va_mask)
+		compute_layout();
+
+	for (i = 0; i < nr_inst; i++) {
+		u32 rd, rn, insn, oinsn;
+
+		/*
+		 * VHE doesn't need any address translation, let's NOP
+		 * everything.
+		 */
+		if (has_vhe()) {
+			updptr[i] = cpu_to_le32(aarch64_insn_gen_nop());
+			continue;
+		}
+
+		oinsn = le32_to_cpu(origptr[i]);
+		rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, oinsn);
+		rn = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RN, oinsn);
+
+		insn = compute_instruction(i, rd, rn);
+		BUG_ON(insn == AARCH64_BREAK_FAULT);
+
+		updptr[i] = cpu_to_le32(insn);
+	}
+}