[PATCH v6 10/12] ARM: KVM: Handle I/O aborts

Christoffer Dall
2012-02-23T07:33:17Z

From: Christoffer Dall <c.dall@virtualopensystems.com>

When the guest accesses I/O memory this will create data abort
exceptions and they are handled by decoding the HSR information
(physical address, read/write, length, register) and forwarding reads
and writes to QEMU which performs the device emulation.

Certain classes of load/store operations do not support the syndrome
information provided in the HSR and we therefore must be able to fetch
the offending instruction from guest memory and decode it manually.

This requires changing the general flow somewhat since new calls to run
the VCPU must check if there's a pending MMIO load and perform the write
after userspace has made the data available.

Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>
---
arch/arm/include/asm/kvm_emulate.h | 2
arch/arm/include/asm/kvm_host.h | 1
arch/arm/include/asm/kvm_mmu.h | 1
arch/arm/kvm/arm.c | 6 +
arch/arm/kvm/emulate.c | 275 ++++++++++++++++++++++++++++++++++++
arch/arm/kvm/mmu.c | 153 ++++++++++++++++++++
arch/arm/kvm/trace.h | 21 +++
7 files changed, 456 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
index 80fe35f..029f45f 100644
--- a/arch/arm/include/asm/kvm_emulate.h
+++ b/arch/arm/include/asm/kvm_emulate.h
@@ -46,6 +46,8 @@ int kvm_handle_cp14_load_store(struct kvm_vcpu *vcpu, struct kvm_run *run);
int kvm_handle_cp14_access(struct kvm_vcpu *vcpu, struct kvm_run *run);
int kvm_handle_cp15_access(struct kvm_vcpu *vcpu, struct kvm_run *run);
int kvm_handle_wfi(struct kvm_vcpu *vcpu, struct kvm_run *run);
+int kvm_emulate_mmio_ls(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
+ unsigned long instr);

/*
* Return the SPSR for the specified mode of the virtual CPU.
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 72ba708..8002903 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -99,6 +99,7 @@ struct kvm_vcpu_arch {
u64 pc_ipa; /* IPA for the current PC (VA to PA result) */

/* IO related fields */
+ bool mmio_sign_extend; /* for byte/halfword loads */
u32 mmio_rd;

/* Interrupt related fields */
diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index b142043..917edd7 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -36,6 +36,7 @@ void free_hyp_pmds(pgd_t *hyp_pgd);
int kvm_alloc_stage2_pgd(struct kvm *kvm);
void kvm_free_stage2_pgd(struct kvm *kvm);

+int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run);

#endif /* __ARM_KVM_MMU_H__ */
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 1566e9d..26fee60 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -425,6 +425,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
int ret = 0;
sigset_t sigsaved;

+ if (run->exit_reason == KVM_EXIT_MMIO) {
+ ret = kvm_handle_mmio_return(vcpu, vcpu->run);
+ if (ret)
+ return ret;
+ }
+
if (vcpu->sigset_active)
sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);

diff --git a/arch/arm/kvm/emulate.c b/arch/arm/kvm/emulate.c
index ea6fa7e..77ccc2b 100644
--- a/arch/arm/kvm/emulate.c
+++ b/arch/arm/kvm/emulate.c
@@ -127,8 +127,30 @@ u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode)
}

/******************************************************************************
- * Co-processor emulation
+ * Utility functions common for all emulation code
+ *****************************************************************************/
+
+/*
+ * This one accepts a matrix where the first element is the
+ * bits as they must be, and the second element is the bitmask.
*/
+#define INSTR_NONE -1
+static int kvm_instr_index(u32 instr, u32 table[][2], int table_entries)
+{
+ int i;
+ u32 mask;
+
+ for (i = 0; i < table_entries; i++) {
+ mask = table[i][1];
+ if ((table[i][0] & mask) == (instr & mask))
+ return i;
+ }
+ return INSTR_NONE;
+}
+
+/******************************************************************************
+ * Co-processor emulation
+ *****************************************************************************/

struct coproc_params {
unsigned long CRm;
@@ -317,3 +339,254 @@ int kvm_handle_wfi(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
return 0;
}
+
+
+/******************************************************************************
+ * Load-Store instruction emulation
+ *****************************************************************************/
+
+/*
+ * Must be ordered with LOADS first and WRITES afterwards
+ * for easy distinction when doing MMIO.
+ */
+#define NUM_LD_INSTR 9
+enum INSTR_LS_INDEXES {
+ INSTR_LS_LDRBT, INSTR_LS_LDRT, INSTR_LS_LDR, INSTR_LS_LDRB,
+ INSTR_LS_LDRD, INSTR_LS_LDREX, INSTR_LS_LDRH, INSTR_LS_LDRSB,
+ INSTR_LS_LDRSH,
+ INSTR_LS_STRBT, INSTR_LS_STRT, INSTR_LS_STR, INSTR_LS_STRB,
+ INSTR_LS_STRD, INSTR_LS_STREX, INSTR_LS_STRH,
+ NUM_LS_INSTR
+};
+
+static u32 ls_instr[NUM_LS_INSTR][2] = {
+ {0x04700000, 0x0d700000}, /* LDRBT */
+ {0x04300000, 0x0d700000}, /* LDRT */
+ {0x04100000, 0x0c500000}, /* LDR */
+ {0x04500000, 0x0c500000}, /* LDRB */
+ {0x000000d0, 0x0e1000f0}, /* LDRD */
+ {0x01900090, 0x0ff000f0}, /* LDREX */
+ {0x001000b0, 0x0e1000f0}, /* LDRH */
+ {0x001000d0, 0x0e1000f0}, /* LDRSB */
+ {0x001000f0, 0x0e1000f0}, /* LDRSH */
+ {0x04600000, 0x0d700000}, /* STRBT */
+ {0x04200000, 0x0d700000}, /* STRT */
+ {0x04000000, 0x0c500000}, /* STR */
+ {0x04400000, 0x0c500000}, /* STRB */
+ {0x000000f0, 0x0e1000f0}, /* STRD */
+ {0x01800090, 0x0ff000f0}, /* STREX */
+ {0x000000b0, 0x0e1000f0} /* STRH */
+};
+
+static inline int get_arm_ls_instr_index(u32 instr)
+{
+ return kvm_instr_index(instr, ls_instr, NUM_LS_INSTR);
+}
+
+/*
+ * Load-Store instruction decoding
+ */
+#define INSTR_LS_TYPE_BIT 26
+#define INSTR_LS_RD_MASK 0x0000f000
+#define INSTR_LS_RD_SHIFT 12
+#define INSTR_LS_RN_MASK 0x000f0000
+#define INSTR_LS_RN_SHIFT 16
+#define INSTR_LS_RM_MASK 0x0000000f
+#define INSTR_LS_OFFSET12_MASK 0x00000fff
+
+#define INSTR_LS_BIT_P 24
+#define INSTR_LS_BIT_U 23
+#define INSTR_LS_BIT_B 22
+#define INSTR_LS_BIT_W 21
+#define INSTR_LS_BIT_L 20
+#define INSTR_LS_BIT_S 6
+#define INSTR_LS_BIT_H 5
+
+/*
+ * ARM addressing mode defines
+ */
+#define OFFSET_IMM_MASK 0x0e000000
+#define OFFSET_IMM_VALUE 0x04000000
+#define OFFSET_REG_MASK 0x0e000ff0
+#define OFFSET_REG_VALUE 0x06000000
+#define OFFSET_SCALE_MASK 0x0e000010
+#define OFFSET_SCALE_VALUE 0x06000000
+
+#define SCALE_SHIFT_MASK 0x000000a0
+#define SCALE_SHIFT_SHIFT 5
+#define SCALE_SHIFT_LSL 0x0
+#define SCALE_SHIFT_LSR 0x1
+#define SCALE_SHIFT_ASR 0x2
+#define SCALE_SHIFT_ROR_RRX 0x3
+#define SCALE_SHIFT_IMM_MASK 0x00000f80
+#define SCALE_SHIFT_IMM_SHIFT 6
+
+#define PSR_BIT_C 29
+
+static unsigned long ls_word_calc_offset(struct kvm_vcpu *vcpu,
+ unsigned long instr)
+{
+ int offset = 0;
+
+ if ((instr & OFFSET_IMM_MASK) == OFFSET_IMM_VALUE) {
+ /* Immediate offset/index */
+ offset = instr & INSTR_LS_OFFSET12_MASK;
+
+ if (!(instr & (1U << INSTR_LS_BIT_U)))
+ offset = -offset;
+ }
+
+ if ((instr & OFFSET_REG_MASK) == OFFSET_REG_VALUE) {
+ /* Register offset/index */
+ u8 rm = instr & INSTR_LS_RM_MASK;
+ offset = *vcpu_reg(vcpu, rm);
+
+ if (!(instr & (1U << INSTR_LS_BIT_P)))
+ offset = 0;
+ }
+
+ if ((instr & OFFSET_SCALE_MASK) == OFFSET_SCALE_VALUE) {
+ /* Scaled register offset */
+ u8 rm = instr & INSTR_LS_RM_MASK;
+ u8 shift = (instr & SCALE_SHIFT_MASK) >> SCALE_SHIFT_SHIFT;
+ u32 shift_imm = (instr & SCALE_SHIFT_IMM_MASK)
+ >> SCALE_SHIFT_IMM_SHIFT;
+ offset = *vcpu_reg(vcpu, rm);
+
+ switch (shift) {
+ case SCALE_SHIFT_LSL:
+ offset = offset << shift_imm;
+ break;
+ case SCALE_SHIFT_LSR:
+ if (shift_imm == 0)
+ offset = 0;
+ else
+ offset = ((u32)offset) >> shift_imm;
+ break;
+ case SCALE_SHIFT_ASR:
+ if (shift_imm == 0) {
+ if (offset & (1U << 31))
+ offset = 0xffffffff;
+ else
+ offset = 0;
+ } else {
+ /* Ensure arithmetic shift */
+ asm("mov %[r], %[op], ASR %[s]":
+ [r] "=r" (offset) :
+ [op] "r" (offset), [s] "r" (shift_imm));
+ }
+ break;
+ case SCALE_SHIFT_ROR_RRX:
+ if (shift_imm == 0) {
+ u32 C = (vcpu->arch.regs.cpsr &
+ (1U << PSR_BIT_C));
+ offset = (C << 31) | offset >> 1;
+ } else {
+ /* Ensure arithmetic shift */
+ asm("mov %[r], %[op], ASR %[s]":
+ [r] "=r" (offset) :
+ [op] "r" (offset), [s] "r" (shift_imm));
+ }
+ break;
+ }
+
+ if (instr & (1U << INSTR_LS_BIT_U))
+ return offset;
+ else
+ return -offset;
+ }
+
+ if (instr & (1U << INSTR_LS_BIT_U))
+ return offset;
+ else
+ return -offset;
+
+ BUG();
+}
+
+static int kvm_ls_length(struct kvm_vcpu *vcpu, u32 instr)
+{
+ int index;
+
+ index = get_arm_ls_instr_index(instr);
+
+ if (instr & (1U << INSTR_LS_TYPE_BIT)) {
+ /* LS word or unsigned byte */
+ if (instr & (1U << INSTR_LS_BIT_B))
+ return sizeof(unsigned char);
+ else
+ return sizeof(u32);
+ } else {
+ /* LS halfword, doubleword or signed byte */
+ u32 H = (instr & (1U << INSTR_LS_BIT_H));
+ u32 S = (instr & (1U << INSTR_LS_BIT_S));
+ u32 L = (instr & (1U << INSTR_LS_BIT_L));
+
+ if (!L && S) {
+ kvm_err("WARNING: d-word for MMIO\n");
+ return 2 * sizeof(u32);
+ } else if (L && S && !H)
+ return sizeof(char);
+ else
+ return sizeof(u16);
+ }
+
+ BUG();
+}
+
+/**
+ * kvm_emulate_mmio_ls - emulates load/store instructions made to I/O memory
+ * @vcpu: The vcpu pointer
+ * @fault_ipa: The IPA that caused the 2nd stage fault
+ * @instr: The instruction that caused the fault
+ *
+ * Handles emulation of load/store instructions which cannot be emulated through
+ * information found in the HSR on faults. It is necessary in this case to
+ * simply decode the offending instruction in software and determine the
+ * required operands.
+ */
+int kvm_emulate_mmio_ls(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
+ unsigned long instr)
+{
+ unsigned long rd, rn, offset, len;
+ int index;
+ bool is_write;
+
+ trace_kvm_mmio_emulate(vcpu->arch.regs.pc, instr, vcpu->arch.regs.cpsr);
+
+ index = get_arm_ls_instr_index(instr);
+ if (index == INSTR_NONE) {
+ kvm_err("Unknown load/store instruction\n");
+ return -EINVAL;
+ }
+
+ is_write = (index < NUM_LD_INSTR) ? false : true;
+ rd = (instr & INSTR_LS_RD_MASK) >> INSTR_LS_RD_SHIFT;
+ len = kvm_ls_length(vcpu, instr);
+
+ vcpu->run->exit_reason = KVM_EXIT_MMIO;
+ vcpu->run->mmio.is_write = is_write;
+ vcpu->run->mmio.phys_addr = fault_ipa;
+ vcpu->run->mmio.len = len;
+ vcpu->arch.mmio_sign_extend = false;
+ vcpu->arch.mmio_rd = rd;
+
+ trace_kvm_mmio((is_write) ? KVM_TRACE_MMIO_WRITE :
+ KVM_TRACE_MMIO_READ_UNSATISFIED,
+ len, fault_ipa, (is_write) ? *vcpu_reg(vcpu, rd) : 0);
+
+ /* Handle base register writeback */
+ if (!(instr & (1U << INSTR_LS_BIT_P)) ||
+ (instr & (1U << INSTR_LS_BIT_W))) {
+ rn = (instr & INSTR_LS_RN_MASK) >> INSTR_LS_RN_SHIFT;
+ offset = ls_word_calc_offset(vcpu, instr);
+ *vcpu_reg(vcpu, rn) += offset;
+ }
+
+ /*
+ * The MMIO instruction is emulated and should not be re-executed
+ * in the guest. (XXX We don't support Thumb instructions yet).
+ */
+ *vcpu_reg(vcpu, 15) += 4;
+ return 0;
+}
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index eb91da2..bbbba44 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -16,9 +16,13 @@

#include <linux/mman.h>
#include <linux/kvm_host.h>
+#include <trace/events/kvm.h>
#include <asm/pgalloc.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_mmu.h>
+#include <asm/kvm_emulate.h>
+
+#include "trace.h"

pgd_t *kvm_hyp_pgd;
DEFINE_MUTEX(kvm_hyp_pgd_mutex);
@@ -337,6 +341,150 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
return ret;
}

+/**
+ * kvm_handle_mmio_return -- Handle MMIO loads after user space emulation
+ * @vcpu: The VCPU pointer
+ * @run: The VCPU run struct containing the mmio data
+ *
+ * This should only be called after returning from userspace for MMIO load
+ * emulation.
+ */
+int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+ int *dest;
+ unsigned int len;
+ int mask;
+
+ if (!run->mmio.is_write) {
+ dest = vcpu_reg(vcpu, vcpu->arch.mmio_rd);
+ memset(dest, 0, sizeof(int));
+
+ len = run->mmio.len;
+ if (len > 4)
+ return -EINVAL;
+
+ memcpy(dest, run->mmio.data, len);
+
+ trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
+ *((u64 *)run->mmio.data));
+
+ if (vcpu->arch.mmio_sign_extend && len < 4) {
+ mask = 1U << ((len * 8) - 1);
+ *dest = (*dest ^ mask) - mask;
+ }
+ }
+
+ return 0;
+}
+
+/**
+ * invalid_io_mem_abort -- Handle I/O aborts ISV bit is clear
+ *
+ * @vcpu: The vcpu pointer
+ * @fault_ipa: The IPA that caused the 2nd stage fault
+ *
+ * Some load/store instructions cannot be emulated using the information
+ * presented in the HSR, for instance, register write-back instructions are not
+ * supported. We therefore need to fetch the instruction, decode it, and then
+ * emulate its behavior.
+ */
+static int invalid_io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
+{
+ unsigned long instr;
+ phys_addr_t pc_ipa;
+
+ if (vcpu->arch.pc_ipa & (1U << 11)) {
+ /* LPAE PAR format */
+ pc_ipa = vcpu->arch.pc_ipa & PAGE_MASK & ((1ULL << 32) - 1);
+ } else {
+ /* VMSAv7 PAR format */
+ pc_ipa = vcpu->arch.pc_ipa & PAGE_MASK & ((1ULL << 40) - 1);
+ }
+ pc_ipa += vcpu->arch.regs.pc & ~PAGE_MASK;
+
+ if (kvm_read_guest(vcpu->kvm, pc_ipa, &instr, sizeof(instr))) {
+ kvm_err("Could not copy guest instruction\n");
+ return -EFAULT;
+ }
+
+ if (vcpu->arch.regs.cpsr & PSR_T_BIT) {
+ /* Need to decode thumb instructions as well */
+ return -EINVAL;
+ }
+
+ return kvm_emulate_mmio_ls(vcpu, fault_ipa, instr);
+}
+
+static int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
+ phys_addr_t fault_ipa, struct kvm_memory_slot *memslot)
+{
+ unsigned long rd, len, instr_len;
+ bool is_write, sign_extend;
+
+ if (!(vcpu->arch.hsr & HSR_ISV))
+ return invalid_io_mem_abort(vcpu, fault_ipa);
+
+ if (((vcpu->arch.hsr >> 8) & 1)) {
+ kvm_err("Not supported, Cache operation on I/O addr.\n");
+ return -EFAULT;
+ }
+
+ if ((vcpu->arch.hsr >> 7) & 1) {
+ kvm_err("Translation table accesses I/O memory\n");
+ return -EFAULT;
+ }
+
+ switch ((vcpu->arch.hsr >> 22) & 0x3) {
+ case 0:
+ len = 1;
+ break;
+ case 1:
+ len = 2;
+ break;
+ case 2:
+ len = 4;
+ break;
+ default:
+ kvm_err("Invalid I/O abort\n");
+ return -EFAULT;
+ }
+
+ is_write = ((vcpu->arch.hsr >> 6) & 1);
+ sign_extend = ((vcpu->arch.hsr >> 21) & 1);
+ rd = (vcpu->arch.hsr >> 16) & 0xf;
+ BUG_ON(rd > 15);
+
+ if (rd == 15) {
+ kvm_err("I/O memory trying to read/write pc\n");
+ return -EFAULT;
+ }
+
+ /* Get instruction length in bytes */
+ instr_len = ((vcpu->arch.hsr >> 25) & 1) ? 4 : 2;
+
+ /* Export MMIO operations to user space */
+ run->exit_reason = KVM_EXIT_MMIO;
+ run->mmio.is_write = is_write;
+ run->mmio.phys_addr = fault_ipa;
+ run->mmio.len = len;
+ vcpu->arch.mmio_sign_extend = sign_extend;
+ vcpu->arch.mmio_rd = rd;
+
+ trace_kvm_mmio((is_write) ? KVM_TRACE_MMIO_WRITE :
+ KVM_TRACE_MMIO_READ_UNSATISFIED,
+ len, fault_ipa, (is_write) ? *vcpu_reg(vcpu, rd) : 0);
+
+ if (is_write)
+ memcpy(run->mmio.data, vcpu_reg(vcpu, rd), len);
+
+ /*
+ * The MMIO instruction is emulated and should not be re-executed
+ * in the guest.
+ */
+ *vcpu_reg(vcpu, 15) += instr_len;
+ return 0;
+}
+
#define HSR_ABT_FS (0x3f)
#define HPFAR_MASK (~0xf)

@@ -382,8 +530,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
return -EFAULT;
}

- kvm_pr_unimpl("I/O address abort...");
- return 0;
+ /* Adjust page offset */
+ fault_ipa += vcpu->arch.hdfar % PAGE_SIZE;
+ return io_mem_abort(vcpu, run, fault_ipa, memslot);
}

memslot = gfn_to_memslot(vcpu->kvm, gfn);
diff --git a/arch/arm/kvm/trace.h b/arch/arm/kvm/trace.h
index e474a0a..bd3a6cc 100644
--- a/arch/arm/kvm/trace.h
+++ b/arch/arm/kvm/trace.h
@@ -39,6 +39,27 @@ TRACE_EVENT(kvm_exit,
TP_printk("PC: 0x%08lx", __entry->vcpu_pc)
);

+TRACE_EVENT(kvm_mmio_emulate,
+ TP_PROTO(unsigned long vcpu_pc, unsigned long instr,
+ unsigned long cpsr),
+ TP_ARGS(vcpu_pc, instr, cpsr),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, vcpu_pc )
+ __field( unsigned long, instr )
+ __field( unsigned long, cpsr )
+ ),
+
+ TP_fast_assign(
+ __entry->vcpu_pc = vcpu_pc;
+ __entry->vcpu_pc = instr;
+ __entry->vcpu_pc = cpsr;
+ ),
+
+ TP_printk("Emulate MMIO at: 0x%08lx (instr: %08lx, cpsr: %08lx)",
+ __entry->vcpu_pc, __entry->instr, __entry->cpsr)
+);
+
/* Architecturally implementation defined CP15 register access */
TRACE_EVENT(kvm_emulate_cp15_imp,
TP_PROTO(unsigned long Op1, unsigned long Rt1, unsigned long CRn,