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migration: Allow postcopy_ram_supported_by_host() to report err
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Instead of print it to STDERR, bring the error upwards so that it can be
reported via QMP responses.

E.g.:

{ "execute": "migrate-set-capabilities" ,
  "arguments": { "capabilities":
  [ { "capability": "postcopy-ram", "state": true } ] } }

{ "error":
  { "class": "GenericError",
    "desc": "Postcopy is not supported: Host backend files need to be TMPFS
    or HUGETLBFS only" } }

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
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@xzpeter
xzpeter authored and Juan Quintela committed Apr 26, 2023
1 parent bf3e8f9 commit 6601591
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Showing 4 changed files with 39 additions and 34 deletions.
8 changes: 3 additions & 5 deletions migration/options.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -302,6 +302,7 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
{
MigrationIncomingState *mis = migration_incoming_get_current();

ERRP_GUARD();
#ifndef CONFIG_LIVE_BLOCK_MIGRATION
if (new_caps[MIGRATION_CAPABILITY_BLOCK]) {
error_setg(errp, "QEMU compiled without old-style (blk/-b, inc/-i) "
Expand All @@ -327,11 +328,8 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
*/
if (!old_caps[MIGRATION_CAPABILITY_POSTCOPY_RAM] &&
runstate_check(RUN_STATE_INMIGRATE) &&
!postcopy_ram_supported_by_host(mis)) {
/* postcopy_ram_supported_by_host will have emitted a more
* detailed message
*/
error_setg(errp, "Postcopy is not supported");
!postcopy_ram_supported_by_host(mis, errp)) {
error_prepend(errp, "Postcopy is not supported: ");
return false;
}

Expand Down
59 changes: 32 additions & 27 deletions migration/postcopy-ram.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -283,19 +283,21 @@ static bool request_ufd_features(int ufd, uint64_t features)
return true;
}

static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis)
static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis,
Error **errp)
{
uint64_t asked_features = 0;
static uint64_t supported_features;

ERRP_GUARD();
/*
* it's not possible to
* request UFFD_API twice per one fd
* userfault fd features is persistent
*/
if (!supported_features) {
if (!receive_ufd_features(&supported_features)) {
error_report("%s failed", __func__);
error_setg(errp, "Userfault feature detection failed");
return false;
}
}
Expand All @@ -317,8 +319,7 @@ static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis)
* userfault file descriptor
*/
if (!request_ufd_features(ufd, asked_features)) {
error_report("%s failed: features %" PRIu64, __func__,
asked_features);
error_setg(errp, "Failed features %" PRIu64, asked_features);
return false;
}

Expand All @@ -329,7 +330,8 @@ static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis)
have_hp = supported_features & UFFD_FEATURE_MISSING_HUGETLBFS;
#endif
if (!have_hp) {
error_report("Userfault on this host does not support huge pages");
error_setg(errp,
"Userfault on this host does not support huge pages");
return false;
}
}
Expand All @@ -338,24 +340,26 @@ static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis)

/* Callback from postcopy_ram_supported_by_host block iterator.
*/
static int test_ramblock_postcopiable(RAMBlock *rb)
static int test_ramblock_postcopiable(RAMBlock *rb, Error **errp)
{
const char *block_name = qemu_ram_get_idstr(rb);
ram_addr_t length = qemu_ram_get_used_length(rb);
size_t pagesize = qemu_ram_pagesize(rb);
QemuFsType fs;

if (length % pagesize) {
error_report("Postcopy requires RAM blocks to be a page size multiple,"
" block %s is 0x" RAM_ADDR_FMT " bytes with a "
"page size of 0x%zx", block_name, length, pagesize);
error_setg(errp,
"Postcopy requires RAM blocks to be a page size multiple,"
" block %s is 0x" RAM_ADDR_FMT " bytes with a "
"page size of 0x%zx", block_name, length, pagesize);
return 1;
}

if (rb->fd >= 0) {
fs = qemu_fd_getfs(rb->fd);
if (fs != QEMU_FS_TYPE_TMPFS && fs != QEMU_FS_TYPE_HUGETLBFS) {
error_report("Host backend files need to be TMPFS or HUGETLBFS only");
error_setg(errp,
"Host backend files need to be TMPFS or HUGETLBFS only");
return 1;
}
}
Expand All @@ -368,7 +372,8 @@ static int test_ramblock_postcopiable(RAMBlock *rb)
* normally fine since if the postcopy succeeds it gets turned back on at the
* end.
*/
bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
bool postcopy_ram_supported_by_host(MigrationIncomingState *mis,
Error **errp)
{
long pagesize = qemu_real_host_page_size();
int ufd = -1;
Expand All @@ -377,29 +382,27 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
struct uffdio_register reg_struct;
struct uffdio_range range_struct;
uint64_t feature_mask;
Error *local_err = NULL;
RAMBlock *block;

ERRP_GUARD();
if (qemu_target_page_size() > pagesize) {
error_report("Target page size bigger than host page size");
error_setg(errp, "Target page size bigger than host page size");
goto out;
}

ufd = uffd_open(O_CLOEXEC);
if (ufd == -1) {
error_report("%s: userfaultfd not available: %s", __func__,
strerror(errno));
error_setg(errp, "Userfaultfd not available: %s", strerror(errno));
goto out;
}

/* Give devices a chance to object */
if (postcopy_notify(POSTCOPY_NOTIFY_PROBE, &local_err)) {
error_report_err(local_err);
if (postcopy_notify(POSTCOPY_NOTIFY_PROBE, errp)) {
goto out;
}

/* Version and features check */
if (!ufd_check_and_apply(ufd, mis)) {
if (!ufd_check_and_apply(ufd, mis, errp)) {
goto out;
}

Expand All @@ -417,7 +420,7 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
* affect in reality, or we can revisit.
*/
RAMBLOCK_FOREACH(block) {
if (test_ramblock_postcopiable(block)) {
if (test_ramblock_postcopiable(block, errp)) {
goto out;
}
}
Expand All @@ -427,7 +430,7 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
* it was enabled.
*/
if (munlockall()) {
error_report("%s: munlockall: %s", __func__, strerror(errno));
error_setg(errp, "munlockall() failed: %s", strerror(errno));
goto out;
}

Expand All @@ -439,8 +442,7 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
testarea = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE |
MAP_ANONYMOUS, -1, 0);
if (testarea == MAP_FAILED) {
error_report("%s: Failed to map test area: %s", __func__,
strerror(errno));
error_setg(errp, "Failed to map test area: %s", strerror(errno));
goto out;
}
g_assert(QEMU_PTR_IS_ALIGNED(testarea, pagesize));
Expand All @@ -450,23 +452,23 @@ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;

if (ioctl(ufd, UFFDIO_REGISTER, &reg_struct)) {
error_report("%s userfault register: %s", __func__, strerror(errno));
error_setg(errp, "UFFDIO_REGISTER failed: %s", strerror(errno));
goto out;
}

range_struct.start = (uintptr_t)testarea;
range_struct.len = pagesize;
if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) {
error_report("%s userfault unregister: %s", __func__, strerror(errno));
error_setg(errp, "UFFDIO_UNREGISTER failed: %s", strerror(errno));
goto out;
}

feature_mask = (__u64)1 << _UFFDIO_WAKE |
(__u64)1 << _UFFDIO_COPY |
(__u64)1 << _UFFDIO_ZEROPAGE;
if ((reg_struct.ioctls & feature_mask) != feature_mask) {
error_report("Missing userfault map features: %" PRIx64,
(uint64_t)(~reg_struct.ioctls & feature_mask));
error_setg(errp, "Missing userfault map features: %" PRIx64,
(uint64_t)(~reg_struct.ioctls & feature_mask));
goto out;
}

Expand Down Expand Up @@ -1188,6 +1190,8 @@ static int postcopy_temp_pages_setup(MigrationIncomingState *mis)

int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
{
Error *local_err = NULL;

/* Open the fd for the kernel to give us userfaults */
mis->userfault_fd = uffd_open(O_CLOEXEC | O_NONBLOCK);
if (mis->userfault_fd == -1) {
Expand All @@ -1200,7 +1204,8 @@ int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
* Although the host check already tested the API, we need to
* do the check again as an ABI handshake on the new fd.
*/
if (!ufd_check_and_apply(mis->userfault_fd, mis)) {
if (!ufd_check_and_apply(mis->userfault_fd, mis, &local_err)) {
error_report_err(local_err);
return -1;
}

Expand Down
3 changes: 2 additions & 1 deletion migration/postcopy-ram.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,8 @@
#define QEMU_POSTCOPY_RAM_H

/* Return true if the host supports everything we need to do postcopy-ram */
bool postcopy_ram_supported_by_host(MigrationIncomingState *mis);
bool postcopy_ram_supported_by_host(MigrationIncomingState *mis,
Error **errp);

/*
* Make all of RAM sensitive to accesses to areas that haven't yet been written
Expand Down
3 changes: 2 additions & 1 deletion migration/savevm.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1753,7 +1753,8 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis,
return -EINVAL;
}

if (!postcopy_ram_supported_by_host(mis)) {
if (!postcopy_ram_supported_by_host(mis, &local_err)) {
error_report_err(local_err);
postcopy_state_set(POSTCOPY_INCOMING_NONE);
return -1;
}
Expand Down

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