[PATCH v3 2/4] kvm: attach the exit reason of vcpu as auxstr to KVM_RUN output
Masatake YAMATO
yamato at redhat.com
Sat Jul 7 07:49:11 UTC 2018
In KVM, a virtual machine implementation like Qemu can access a vcpu
via ioctl. KVM_RUN is an ioctl command to enter vcpu. The command
returns control for various reasons: needs of device emulation or
consuming time slices are the typical ones. The vmi takes a different
action for the reason.
We, strace users, want to know the reason to understand kvm. This
change prints the reason as auxstr if "-e kvm=vcpu" option is given,
and if strace runs on Linux 4.16.0 or higher, which includes commit
e46b469278a59781f9b25ff608af84892963821b, "kvm: embed vcpu id to dentry
of vcpu anon inode."
The way to get the reason is a bit complicated because the ioctl does
not return it to the userspace directly. Instead, the vmi and kvm
communicate via an area of the process virtual memory where the fd of
vcpu is mmap'ed. strace must peek the area to know the reason.
The change does three things: (1) recording the area for the given vcpu
when the target calls VCPU_CREATE to vcpu_info_list per tcb data field,
(2) verifying the data recorded in vcpu_info_list before doing (3), and
(3) decoding the exit reason field of the area.
The change is complicated because there is a case that strace
does not have a chance to do (1) if -p option is used.
In this case, vcpu_info data created in the step (2).
The area has more fields than "exit reason",
dumping them may be implemented in the future.
* defs.h (struct tcb) [HAVE_LINUX_KVM_H]: Add vcpu_info_list field.
[HAVE_LINUX_KVM_H]: (kvm_run_structure_decoder_init,
kvm_vcpu_info_free): New declarations.
* strace.c (usage): Add "kvm" as a new expression for -e option.
(droptcb): Call kvm_vcpu_info_free.
* filter_qualify.c (qualify_kvm): New function calling
kvm_run_structure_decoder_init to enable for attaching the exit
reason to auxstr.
(qual_options): Add "kvm" as an entry.
* xlat/kvm_exit_reason.in: New file.
* kvm.c: Include xmalloc.h and mmap_cache.h.
(dump_kvm_run_structure): New static variable.
(kvm_run_structure_decoder_init): New function.
(vcpu_info): New struct definition representing the 3-tuple: vcpu file
descriptor, id of the vcpu, and mmap'ed entry.
(vcpu_find, vcpu_alloc, vcpu_register, vcpu_getinfo,
kvm_vcpu_info_free): New functions to access tcb's vcpu_info_list
field and vcpu_info data type.
(is_map_for_file, map_len): New helper functions.
(kvm_ioclt_run_attach_auxstr, kvm_ioctl_decode_run): New functions
decoding vcpu exit reason and attaching the decoded data to auxstr
field of tcb.
(kvm_ioctl_create_vcpu): Call vcpu_register to make an entry mapping
a file descriptor and the vcpu id associated with the fd.
(kvm_ioctl): Call kvm_ioctl_decode_run.
Signed-off-by: Masatake YAMATO <yamato at redhat.com>
Co-Authored-by: Dmitry V. Levin <ldv at altlinux.org>
---
defs.h | 9 ++
filter_qualify.c | 19 ++++
kvm.c | 221 +++++++++++++++++++++++++++++++++++++++-
strace.c | 10 +-
xlat/kvm_exit_reason.in | 30 ++++++
5 files changed, 287 insertions(+), 2 deletions(-)
create mode 100644 xlat/kvm_exit_reason.in
diff --git a/defs.h b/defs.h
index 4437d6fb..0d4bf82b 100644
--- a/defs.h
+++ b/defs.h
@@ -236,6 +236,10 @@ struct tcb {
struct mmap_cache_t *mmap_cache;
+#ifdef HAVE_LINUX_KVM_H
+ struct vcpu_info *vcpu_info_list;
+#endif
+
#ifdef ENABLE_STACKTRACE
void *unwind_ctx;
struct unwind_queue_t *unwind_queue;
@@ -988,6 +992,11 @@ extern void unwind_tcb_print(struct tcb *);
extern void unwind_tcb_capture(struct tcb *);
#endif
+#ifdef HAVE_LINUX_KVM_H
+extern void kvm_run_structure_decoder_init(void);
+extern void kvm_vcpu_info_free(struct tcb *);
+#endif
+
static inline int
printstrn(struct tcb *tcp, kernel_ulong_t addr, kernel_ulong_t len)
{
diff --git a/filter_qualify.c b/filter_qualify.c
index 9b5569c3..e9304e89 100644
--- a/filter_qualify.c
+++ b/filter_qualify.c
@@ -405,6 +405,22 @@ qualify_inject(const char *const str)
qualify_inject_common(str, false, "inject argument");
}
+#ifdef HAVE_LINUX_KVM_H
+static void
+qualify_kvm(const char *const str)
+{
+ if (strcmp(str, "vcpu") == 0)
+ {
+ if (os_release >= KERNEL_VERSION(4, 16, 0))
+ kvm_run_structure_decoder_init();
+ else
+ error_msg("-e kvm=vcpu option needs Linux 4.16.0 or higher");
+ }
+ else
+ error_msg("unknown value for -e kvm= option: %s", str);
+}
+#endif
+
static const struct qual_options {
const char *name;
void (*qualify)(const char *);
@@ -428,6 +444,9 @@ static const struct qual_options {
{ "w", qualify_write },
{ "fault", qualify_fault },
{ "inject", qualify_inject },
+#ifdef HAVE_LINUX_KVM_H
+ { "kvm", qualify_kvm },
+#endif
};
void
diff --git a/kvm.c b/kvm.c
index 86fd9e50..c90be839 100644
--- a/kvm.c
+++ b/kvm.c
@@ -34,13 +34,175 @@
# include <linux/kvm.h>
# include "print_fields.h"
# include "arch_kvm.c"
+# include "xmalloc.h"
+# include "mmap_cache.h"
+
+struct vcpu_info {
+ struct vcpu_info *next;
+ int fd;
+ int cpuid;
+ long mmap_addr;
+ unsigned long mmap_len;
+ bool resolved;
+};
+
+static bool dump_kvm_run_structure;
+
+static struct vcpu_info *
+vcpu_find(struct tcb *const tcp, int fd)
+{
+ for (struct vcpu_info *vcpu_info = tcp->vcpu_info_list;
+ vcpu_info;
+ vcpu_info = vcpu_info->next)
+ if (vcpu_info->fd == fd)
+ return vcpu_info;
+
+ return NULL;
+}
+
+static struct vcpu_info *
+vcpu_alloc(struct tcb *const tcp, int fd, int cpuid)
+{
+ struct vcpu_info *vcpu_info = xcalloc(1, sizeof(*vcpu_info));
+
+ vcpu_info->fd = fd;
+ vcpu_info->cpuid = cpuid;
+
+ vcpu_info->next = tcp->vcpu_info_list;
+ tcp->vcpu_info_list = vcpu_info;
+
+ return vcpu_info;
+}
+
+void
+kvm_vcpu_info_free(struct tcb *tcp)
+{
+ struct vcpu_info *head, *next;
+
+ for (head = tcp->vcpu_info_list; head; head = next) {
+ next = head->next;
+ free(head);
+ }
+
+ tcp->vcpu_info_list = NULL;
+}
+
+static void
+vcpu_register(struct tcb *const tcp, int fd, int cpuid)
+{
+ if (fd < 0)
+ return;
+
+ struct vcpu_info *vcpu_info = vcpu_find(tcp, fd);
+
+ if (!vcpu_info)
+ vcpu_info = vcpu_alloc(tcp, fd, cpuid);
+ else if (vcpu_info->cpuid != cpuid)
+ {
+ vcpu_info->cpuid = cpuid;
+ vcpu_info->resolved = false;
+ }
+}
+
+static bool
+is_map_for_file(struct mmap_cache_entry_t *map_info, void *data)
+{
+ /* major version for anon inode may be given in get_anon_bdev()
+ * in linux kernel.
+ *
+ * *p = MKDEV(0, dev & MINORMASK);
+ *-----------------^
+ */
+ return map_info->binary_filename &&
+ map_info->major == 0 &&
+ strcmp(map_info->binary_filename, data) == 0;
+}
+
+static unsigned long
+map_len(struct mmap_cache_entry_t *map_info)
+{
+ return map_info->start_addr < map_info->end_addr
+ ? map_info->end_addr - map_info->start_addr
+ : 0;
+}
+
+#define VCPU_DENTRY_PREFIX "anon_inode:kvm-vcpu:"
+
+static struct vcpu_info*
+vcpu_get_info(struct tcb *const tcp, int fd)
+{
+ struct vcpu_info *vcpu_info = vcpu_find(tcp, fd);
+ struct mmap_cache_entry_t *map_info;
+ const char *cpuid_str;
+
+ enum mmap_cache_rebuild_result mc_stat =
+ mmap_cache_rebuild_if_invalid(tcp, __func__);
+ if (mc_stat == MMAP_CACHE_REBUILD_NOCACHE)
+ return NULL;
+
+ if (vcpu_info && vcpu_info->resolved) {
+ if (mc_stat == MMAP_CACHE_REBUILD_READY)
+ return vcpu_info;
+ else {
+ map_info = mmap_cache_search(tcp, vcpu_info->mmap_addr);
+ if (map_info) {
+ cpuid_str =
+ STR_STRIP_PREFIX(map_info->binary_filename,
+ VCPU_DENTRY_PREFIX);
+ if (cpuid_str != map_info->binary_filename) {
+ int cpuid = string_to_uint(cpuid_str);
+ if (cpuid < 0)
+ return NULL;
+ if (vcpu_info->cpuid == cpuid)
+ return vcpu_info;
+ }
+ }
+
+ /* The vcpu vma may be mremap'ed. */
+ vcpu_info->resolved = false;
+ }
+ }
+
+ /* Slow path: !vcpu_info || !vcpu_info->resolved */
+ char path[PATH_MAX + 1];
+ cpuid_str = path;
+ if (getfdpath(tcp, fd, path, sizeof(path)) >= 0)
+ cpuid_str = STR_STRIP_PREFIX(path, VCPU_DENTRY_PREFIX);
+ if (cpuid_str == path)
+ map_info = NULL;
+ else
+ map_info = mmap_cache_search_custom(tcp, is_map_for_file, path);
+
+ if (map_info) {
+ int cpuid = string_to_uint(cpuid_str);
+ if (cpuid < 0)
+ return NULL;
+ if (!vcpu_info)
+ vcpu_info = vcpu_alloc(tcp, fd, cpuid);
+ else if (vcpu_info->cpuid != cpuid)
+ vcpu_info->cpuid = cpuid;
+ vcpu_info->mmap_addr = map_info->start_addr;
+ vcpu_info->mmap_len = map_len(map_info);
+ vcpu_info->resolved = true;
+ return vcpu_info;
+ }
+
+ return NULL;
+}
static int
kvm_ioctl_create_vcpu(struct tcb *const tcp, const kernel_ulong_t arg)
{
uint32_t cpuid = arg;
- tprintf(", %u", cpuid);
+ if (entering(tcp)) {
+ tprintf(", %u", cpuid);
+ if (dump_kvm_run_structure)
+ return 0;
+ } else if (!syserror(tcp)) {
+ vcpu_register(tcp, tcp->u_rval, cpuid);
+ }
+
return RVAL_IOCTL_DECODED | RVAL_FD;
}
@@ -103,6 +265,53 @@ kvm_ioctl_decode_sregs(struct tcb *const tcp, const unsigned int code,
}
# endif /* HAVE_STRUCT_KVM_SREGS */
+# include "xlat/kvm_exit_reason.h"
+static void
+kvm_ioctl_run_attach_auxstr(struct tcb *const tcp,
+ struct vcpu_info *info)
+
+{
+ static struct kvm_run vcpu_run_struct;
+
+ if (info->mmap_len < sizeof(vcpu_run_struct))
+ return;
+
+ if (umove(tcp, info->mmap_addr, &vcpu_run_struct) < 0)
+ return;
+
+ tcp->auxstr = xlat_idx(kvm_exit_reason, ARRAY_SIZE(kvm_exit_reason) - 1,
+ vcpu_run_struct.exit_reason);
+ if (!tcp->auxstr)
+ tcp->auxstr = "KVM_EXIT_???";
+}
+
+static int
+kvm_ioctl_decode_run(struct tcb *const tcp)
+{
+
+ if (entering(tcp))
+ return 0;
+
+ int r = RVAL_DECODED;
+
+ if (syserror(tcp))
+ return r;
+
+ if (dump_kvm_run_structure) {
+ tcp->auxstr = NULL;
+ int fd = tcp->u_arg[0];
+ struct vcpu_info *info = vcpu_get_info(tcp, fd);
+
+ if (info) {
+ kvm_ioctl_run_attach_auxstr(tcp, info);
+ if (tcp->auxstr)
+ r |= RVAL_STR;
+ }
+ }
+
+ return r;
+}
+
int
kvm_ioctl(struct tcb *const tcp, const unsigned int code, const kernel_ulong_t arg)
{
@@ -129,7 +338,10 @@ kvm_ioctl(struct tcb *const tcp, const unsigned int code, const kernel_ulong_t a
case KVM_CREATE_VM:
return RVAL_DECODED | RVAL_FD;
+
case KVM_RUN:
+ return kvm_ioctl_decode_run(tcp);
+
case KVM_GET_VCPU_MMAP_SIZE:
case KVM_GET_API_VERSION:
default:
@@ -137,4 +349,11 @@ kvm_ioctl(struct tcb *const tcp, const unsigned int code, const kernel_ulong_t a
}
}
+void
+kvm_run_structure_decoder_init(void)
+{
+ dump_kvm_run_structure = true;
+ mmap_cache_enable();
+}
+
#endif /* HAVE_LINUX_KVM_H */
diff --git a/strace.c b/strace.c
index 4b374857..467e8a6e 100644
--- a/strace.c
+++ b/strace.c
@@ -278,7 +278,11 @@ Statistics:\n\
\n\
Filtering:\n\
-e expr a qualifying expression: option=[!]all or option=[!]val1[,val2]...\n\
- options: trace, abbrev, verbose, raw, signal, read, write, fault\n\
+ options: trace, abbrev, verbose, raw, signal, read, write, fault"
+#ifdef HAVE_LINUX_KVM_H
+ ", kvm"
+#endif
+"\n\
-P path trace accesses to path\n\
\n\
Tracing:\n\
@@ -819,6 +823,10 @@ droptcb(struct tcb *tcp)
unwind_tcb_fin(tcp);
#endif
+#ifdef HAVE_LINUX_KVM_H
+ kvm_vcpu_info_free(tcp);
+#endif
+
if (tcp->mmap_cache)
tcp->mmap_cache->free_fn(tcp, __func__);
diff --git a/xlat/kvm_exit_reason.in b/xlat/kvm_exit_reason.in
new file mode 100644
index 00000000..d2b24687
--- /dev/null
+++ b/xlat/kvm_exit_reason.in
@@ -0,0 +1,30 @@
+#value_indexed
+KVM_EXIT_UNKNOWN 0
+KVM_EXIT_EXCEPTION 1
+KVM_EXIT_IO 2
+KVM_EXIT_HYPERCALL 3
+KVM_EXIT_DEBUG 4
+KVM_EXIT_HLT 5
+KVM_EXIT_MMIO 6
+KVM_EXIT_IRQ_WINDOW_OPEN 7
+KVM_EXIT_SHUTDOWN 8
+KVM_EXIT_FAIL_ENTRY 9
+KVM_EXIT_INTR 10
+KVM_EXIT_SET_TPR 11
+KVM_EXIT_TPR_ACCESS 12
+KVM_EXIT_S390_SIEIC 13
+KVM_EXIT_S390_RESET 14
+/* deprecated */
+KVM_EXIT_DCR 15
+KVM_EXIT_NMI 16
+KVM_EXIT_INTERNAL_ERROR 17
+KVM_EXIT_OSI 18
+KVM_EXIT_PAPR_HCALL 19
+KVM_EXIT_S390_UCONTROL 20
+KVM_EXIT_WATCHDOG 21
+KVM_EXIT_S390_TSCH 22
+KVM_EXIT_EPR 23
+KVM_EXIT_SYSTEM_EVENT 24
+KVM_EXIT_S390_STSI 25
+KVM_EXIT_IOAPIC_EOI 26
+KVM_EXIT_HYPERV 27
--
2.17.1
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