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Revert "arm/kvm: add support for MTE"
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This reverts commit b320e21,
which accidentally broke TCG, because it made the TCG -cpu max
report the presence of MTE to the guest even if the board hadn't
enabled MTE by wiring up the tag RAM. This meant that if the guest
then tried to use MTE QEMU would segfault accessing the
non-existent tag RAM:

    ==346473==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address (pc 0x55f328952a4a bp 0x00000213a400 sp 0x7f7871859b80 T346476)
    ==346473==The signal is caused by a READ memory access.
    ==346473==Hint: this fault was caused by a dereference of a high value address (see register values below).  Disassemble the provided pc to learn which register was used.
        #0 0x55f328952a4a in address_space_to_flatview /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/memory.h:1108:12
        #1 0x55f328952a4a in address_space_translate /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/memory.h:2797:31
        #2 0x55f328952a4a in allocation_tag_mem /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang/../../target/arm/tcg/mte_helper.c:176:10
        #3 0x55f32895366c in helper_stgm /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang/../../target/arm/tcg/mte_helper.c:461:15
        #4 0x7f782431a293  (<unknown module>)

It's also not clear that the KVM logic is correct either:
MTE defaults to on there, rather than being only on if the
board wants it on.

Revert the whole commit for now so we can sort out the issues.

(We didn't catch this in CI because we have no test cases in
avocado that use guests with MTE support.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230519145808.348701-1-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
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@pm215 @rth7680
pm215 authored and rth7680 committed May 19, 2023
1 parent 449d6d9 commit d009607
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Showing 6 changed files with 34 additions and 107 deletions.
69 changes: 30 additions & 39 deletions hw/arm/virt.c
View file
Expand Up @@ -2146,7 +2146,7 @@ static void machvirt_init(MachineState *machine)
exit(1);
}

if (vms->mte && hvf_enabled()) {
if (vms->mte && (kvm_enabled() || hvf_enabled())) {
error_report("mach-virt: %s does not support providing "
"MTE to the guest CPU",
current_accel_name());
Expand Down Expand Up @@ -2216,48 +2216,39 @@ static void machvirt_init(MachineState *machine)
}

if (vms->mte) {
if (tcg_enabled()) {
/* Create the memory region only once, but link to all cpus. */
if (!tag_sysmem) {
/*
* The property exists only if MemTag is supported.
* If it is, we must allocate the ram to back that up.
*/
if (!object_property_find(cpuobj, "tag-memory")) {
error_report("MTE requested, but not supported "
"by the guest CPU");
exit(1);
}

tag_sysmem = g_new(MemoryRegion, 1);
memory_region_init(tag_sysmem, OBJECT(machine),
"tag-memory", UINT64_MAX / 32);

if (vms->secure) {
secure_tag_sysmem = g_new(MemoryRegion, 1);
memory_region_init(secure_tag_sysmem, OBJECT(machine),
"secure-tag-memory",
UINT64_MAX / 32);

/* As with ram, secure-tag takes precedence over tag. */
memory_region_add_subregion_overlap(secure_tag_sysmem,
0, tag_sysmem, -1);
}
/* Create the memory region only once, but link to all cpus. */
if (!tag_sysmem) {
/*
* The property exists only if MemTag is supported.
* If it is, we must allocate the ram to back that up.
*/
if (!object_property_find(cpuobj, "tag-memory")) {
error_report("MTE requested, but not supported "
"by the guest CPU");
exit(1);
}

object_property_set_link(cpuobj, "tag-memory",
OBJECT(tag_sysmem), &error_abort);
tag_sysmem = g_new(MemoryRegion, 1);
memory_region_init(tag_sysmem, OBJECT(machine),
"tag-memory", UINT64_MAX / 32);

if (vms->secure) {
object_property_set_link(cpuobj, "secure-tag-memory",
OBJECT(secure_tag_sysmem),
&error_abort);
}
} else if (kvm_enabled()) {
if (!kvm_arm_mte_supported()) {
error_report("MTE requested, but not supported by KVM");
exit(1);
secure_tag_sysmem = g_new(MemoryRegion, 1);
memory_region_init(secure_tag_sysmem, OBJECT(machine),
"secure-tag-memory", UINT64_MAX / 32);

/* As with ram, secure-tag takes precedence over tag. */
memory_region_add_subregion_overlap(secure_tag_sysmem, 0,
tag_sysmem, -1);
}
kvm_arm_enable_mte(cpuobj, &error_abort);
}

object_property_set_link(cpuobj, "tag-memory", OBJECT(tag_sysmem),
&error_abort);
if (vms->secure) {
object_property_set_link(cpuobj, "secure-tag-memory",
OBJECT(secure_tag_sysmem),
&error_abort);
}
}

Expand Down
9 changes: 4 additions & 5 deletions target/arm/cpu.c
View file
Expand Up @@ -1480,7 +1480,6 @@ void arm_cpu_post_init(Object *obj)
qdev_prop_allow_set_link_before_realize,
OBJ_PROP_LINK_STRONG);
}
cpu->has_mte = true;
}
#endif
}
Expand Down Expand Up @@ -1617,7 +1616,7 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
}
if (cpu->tag_memory) {
error_setg(errp,
"Cannot enable %s when guest CPUs has tag memory enabled",
"Cannot enable %s when guest CPUs has MTE enabled",
current_accel_name());
return;
}
Expand Down Expand Up @@ -1997,10 +1996,10 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
}

#ifndef CONFIG_USER_ONLY
if (!cpu->has_mte && cpu_isar_feature(aa64_mte, cpu)) {
if (cpu->tag_memory == NULL && cpu_isar_feature(aa64_mte, cpu)) {
/*
* Disable the MTE feature bits if we do not have the feature
* setup by the machine.
* Disable the MTE feature bits if we do not have tag-memory
* provided by the machine.
*/
cpu->isar.id_aa64pfr1 =
FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 0);
Expand Down
4 changes: 0 additions & 4 deletions target/arm/cpu.h
View file
Expand Up @@ -935,9 +935,6 @@ struct ArchCPU {
*/
uint32_t psci_conduit;

/* CPU has Memory Tag Extension */
bool has_mte;

/* For v8M, initial value of the Secure VTOR */
uint32_t init_svtor;
/* For v8M, initial value of the Non-secure VTOR */
Expand Down Expand Up @@ -1056,7 +1053,6 @@ struct ArchCPU {
bool prop_pauth;
bool prop_pauth_impdef;
bool prop_lpa2;
OnOffAuto prop_mte;

/* DCZ blocksize, in log_2(words), ie low 4 bits of DCZID_EL0 */
uint32_t dcz_blocksize;
Expand Down
35 changes: 0 additions & 35 deletions target/arm/kvm.c
View file
Expand Up @@ -31,7 +31,6 @@
#include "hw/boards.h"
#include "hw/irq.h"
#include "qemu/log.h"
#include "migration/blocker.h"

const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
KVM_CAP_LAST_INFO
Expand Down Expand Up @@ -1065,37 +1064,3 @@ bool kvm_arch_cpu_check_are_resettable(void)
void kvm_arch_accel_class_init(ObjectClass *oc)
{
}

void kvm_arm_enable_mte(Object *cpuobj, Error **errp)
{
static bool tried_to_enable;
static bool succeeded_to_enable;
Error *mte_migration_blocker = NULL;
int ret;

if (!tried_to_enable) {
/*
* MTE on KVM is enabled on a per-VM basis (and retrying doesn't make
* sense), and we only want a single migration blocker as well.
*/
tried_to_enable = true;

ret = kvm_vm_enable_cap(kvm_state, KVM_CAP_ARM_MTE, 0);
if (ret) {
error_setg_errno(errp, -ret, "Failed to enable KVM_CAP_ARM_MTE");
return;
}

/* TODO: add proper migration support with MTE enabled */
error_setg(&mte_migration_blocker,
"Live migration disabled due to MTE enabled");
if (migrate_add_blocker(mte_migration_blocker, errp)) {
error_free(mte_migration_blocker);
return;
}
succeeded_to_enable = true;
}
if (succeeded_to_enable) {
object_property_set_bool(cpuobj, "has_mte", true, NULL);
}
}
5 changes: 0 additions & 5 deletions target/arm/kvm64.c
View file
Expand Up @@ -756,11 +756,6 @@ bool kvm_arm_steal_time_supported(void)
return kvm_check_extension(kvm_state, KVM_CAP_STEAL_TIME);
}

bool kvm_arm_mte_supported(void)
{
return kvm_check_extension(kvm_state, KVM_CAP_ARM_MTE);
}

QEMU_BUILD_BUG_ON(KVM_ARM64_SVE_VQ_MIN != 1);

uint32_t kvm_arm_sve_get_vls(CPUState *cs)
Expand Down
19 changes: 0 additions & 19 deletions target/arm/kvm_arm.h
View file
Expand Up @@ -313,13 +313,6 @@ bool kvm_arm_pmu_supported(void);
*/
bool kvm_arm_sve_supported(void);

/**
* kvm_arm_mte_supported:
*
* Returns: true if KVM can enable MTE, and false otherwise.
*/
bool kvm_arm_mte_supported(void);

/**
* kvm_arm_get_max_vm_ipa_size:
* @ms: Machine state handle
Expand Down Expand Up @@ -384,8 +377,6 @@ void kvm_arm_pvtime_init(CPUState *cs, uint64_t ipa);

int kvm_arm_set_irq(int cpu, int irqtype, int irq, int level);

void kvm_arm_enable_mte(Object *cpuobj, Error **errp);

#else

/*
Expand All @@ -412,11 +403,6 @@ static inline bool kvm_arm_steal_time_supported(void)
return false;
}

static inline bool kvm_arm_mte_supported(void)
{
return false;
}

/*
* These functions should never actually be called without KVM support.
*/
Expand Down Expand Up @@ -465,11 +451,6 @@ static inline uint32_t kvm_arm_sve_get_vls(CPUState *cs)
g_assert_not_reached();
}

static inline void kvm_arm_enable_mte(Object *cpuobj, Error **errp)
{
g_assert_not_reached();
}

#endif

static inline const char *gic_class_name(void)
Expand Down

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