dyntrans.c

/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * KVM/MIPS: Binary Patching for privileged instructions, reduces traps.
 *
 * Copyright (C) 2012  MIPS Technologies, Inc.  All rights reserved.
 * Authors: Sanjay Lal <sanjayl@kymasys.com>
 */

#include <linux/errno.h>
#include <linux/err.h>
#include <linux/highmem.h>
#include <linux/kvm_host.h>
#include <linux/uaccess.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/bootmem.h>
#include <asm/cacheflush.h>

#include "commpage.h"

/**
 * kvm_mips_trans_replace() - Replace trapping instruction in guest memory.
 * @vcpu:	Virtual CPU.
 * @opc:	PC of instruction to replace.
 * @replace:	Instruction to write
 */
static int kvm_mips_trans_replace(struct kvm_vcpu *vcpu, u32 *opc,
				  union mips_instruction replace)
{
	unsigned long vaddr = (unsigned long)opc;
	int err;

retry:
	/* The GVA page table is still active so use the Linux TLB handlers */
	kvm_trap_emul_gva_lockless_begin(vcpu);
	err = put_user(replace.word, opc);
	kvm_trap_emul_gva_lockless_end(vcpu);

	if (unlikely(err)) {
		/*
		 * We write protect clean pages in GVA page table so normal
		 * Linux TLB mod handler doesn't silently dirty the page.
		 * Its also possible we raced with a GVA invalidation.
		 * Try to force the page to become dirty.
		 */
		err = kvm_trap_emul_gva_fault(vcpu, vaddr, true);
		if (unlikely(err)) {
			kvm_info("%s: Address unwriteable: %p\n",
				 __func__, opc);
			return -EFAULT;
		}

		/*
		 * Try again. This will likely trigger a TLB refill, which will
		 * fetch the new dirty entry from the GVA page table, which
		 * should then succeed.
		 */
		goto retry;
	}
	__local_flush_icache_user_range(vaddr, vaddr + 4);

	return 0;
}

int kvm_mips_trans_cache_index(union mips_instruction inst, u32 *opc,
			       struct kvm_vcpu *vcpu)
{
	union mips_instruction nop_inst = { 0 };

	/* Replace the CACHE instruction, with a NOP */
	return kvm_mips_trans_replace(vcpu, opc, nop_inst);
}

/*
 * Address based CACHE instructions are transformed into synci(s). A little
 * heavy for just D-cache invalidates, but avoids an expensive trap
 */
int kvm_mips_trans_cache_va(union mips_instruction inst, u32 *opc,
			    struct kvm_vcpu *vcpu)
{
	union mips_instruction synci_inst = { 0 };

	synci_inst.i_format.opcode = bcond_op;
	synci_inst.i_format.rs = inst.i_format.rs;
	synci_inst.i_format.rt = synci_op;
	if (cpu_has_mips_r6)
		synci_inst.i_format.simmediate = inst.spec3_format.simmediate;
	else
		synci_inst.i_format.simmediate = inst.i_format.simmediate;

	return kvm_mips_trans_replace(vcpu, opc, synci_inst);
}

int kvm_mips_trans_mfc0(union mips_instruction inst, u32 *opc,
			struct kvm_vcpu *vcpu)
{
	union mips_instruction mfc0_inst = { 0 };
	u32 rd, sel;

	rd = inst.c0r_format.rd;
	sel = inst.c0r_format.sel;

	if (rd == MIPS_CP0_ERRCTL && sel == 0) {
		mfc0_inst.r_format.opcode = spec_op;
		mfc0_inst.r_format.rd = inst.c0r_format.rt;
		mfc0_inst.r_format.func = add_op;
	} else {
		mfc0_inst.i_format.opcode = lw_op;
		mfc0_inst.i_format.rt = inst.c0r_format.rt;
		mfc0_inst.i_format.simmediate = KVM_GUEST_COMMPAGE_ADDR |
			offsetof(struct kvm_mips_commpage, cop0.reg[rd][sel]);
#ifdef CONFIG_CPU_BIG_ENDIAN
		if (sizeof(vcpu->arch.cop0->reg[0][0]) == 8)
			mfc0_inst.i_format.simmediate |= 4;
#endif
	}

	return kvm_mips_trans_replace(vcpu, opc, mfc0_inst);
}

int kvm_mips_trans_mtc0(union mips_instruction inst, u32 *opc,
			struct kvm_vcpu *vcpu)
{
	union mips_instruction mtc0_inst = { 0 };
	u32 rd, sel;

	rd = inst.c0r_format.rd;
	sel = inst.c0r_format.sel;

	mtc0_inst.i_format.opcode = sw_op;
	mtc0_inst.i_format.rt = inst.c0r_format.rt;
	mtc0_inst.i_format.simmediate = KVM_GUEST_COMMPAGE_ADDR |
		offsetof(struct kvm_mips_commpage, cop0.reg[rd][sel]);
#ifdef CONFIG_CPU_BIG_ENDIAN
	if (sizeof(vcpu->arch.cop0->reg[0][0]) == 8)
		mtc0_inst.i_format.simmediate |= 4;
#endif

	return kvm_mips_trans_replace(vcpu, opc, mtc0_inst);
}