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KVM: s390: Fix storage attributes migration with memory slots
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This is a fix for several issues that were found in the original code
for storage attributes migration.

Now no bitmap is allocated to keep track of dirty storage attributes;
the extra bits of the per-memslot bitmap that are always present anyway
are now used for this purpose.

The code has also been refactored a little to improve readability.

Fixes: 190df4a ("KVM: s390: CMMA tracking, ESSA emulation, migration mode")
Fixes: 4036e38 ("KVM: s390: ioctls to get and set guest storage attributes")
Acked-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Message-Id: <1525106005-13931-3-git-send-email-imbrenda@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
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Claudio Imbrenda authored and Christian Borntraeger committed Jul 13, 2018
1 parent 0313334 commit afdad61
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Showing 3 changed files with 195 additions and 135 deletions.
9 changes: 2 additions & 7 deletions arch/s390/include/asm/kvm_host.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -793,12 +793,6 @@ struct kvm_s390_vsie {
struct page *pages[KVM_MAX_VCPUS];
};

struct kvm_s390_migration_state {
unsigned long bitmap_size; /* in bits (number of guest pages) */
atomic64_t dirty_pages; /* number of dirty pages */
unsigned long *pgste_bitmap;
};

struct kvm_arch{
void *sca;
int use_esca;
Expand Down Expand Up @@ -828,7 +822,8 @@ struct kvm_arch{
struct kvm_s390_vsie vsie;
u8 epdx;
u64 epoch;
struct kvm_s390_migration_state *migration_state;
int migration_mode;
atomic64_t cmma_dirty_pages;
/* subset of available cpu features enabled by user space */
DECLARE_BITMAP(cpu_feat, KVM_S390_VM_CPU_FEAT_NR_BITS);
struct kvm_s390_gisa *gisa;
Expand Down
293 changes: 174 additions & 119 deletions arch/s390/kvm/kvm-s390.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -862,54 +862,37 @@ static void kvm_s390_sync_request_broadcast(struct kvm *kvm, int req)
*/
static int kvm_s390_vm_start_migration(struct kvm *kvm)
{
struct kvm_s390_migration_state *mgs;
struct kvm_memory_slot *ms;
/* should be the only one */
struct kvm_memslots *slots;
unsigned long ram_pages;
unsigned long ram_pages = 0;
int slotnr;

/* migration mode already enabled */
if (kvm->arch.migration_state)
if (kvm->arch.migration_mode)
return 0;

slots = kvm_memslots(kvm);
if (!slots || !slots->used_slots)
return -EINVAL;

mgs = kzalloc(sizeof(*mgs), GFP_KERNEL);
if (!mgs)
return -ENOMEM;
kvm->arch.migration_state = mgs;

if (kvm->arch.use_cmma) {
if (!kvm->arch.use_cmma) {
kvm->arch.migration_mode = 1;
return 0;
}
/* mark all the pages in active slots as dirty */
for (slotnr = 0; slotnr < slots->used_slots; slotnr++) {
ms = slots->memslots + slotnr;
/*
* Get the first slot. They are reverse sorted by base_gfn, so
* the first slot is also the one at the end of the address
* space. We have verified above that at least one slot is
* present.
* The second half of the bitmap is only used on x86,
* and would be wasted otherwise, so we put it to good
* use here to keep track of the state of the storage
* attributes.
*/
ms = slots->memslots;
/* round up so we only use full longs */
ram_pages = roundup(ms->base_gfn + ms->npages, BITS_PER_LONG);
/* allocate enough bytes to store all the bits */
mgs->pgste_bitmap = vmalloc(ram_pages / 8);
if (!mgs->pgste_bitmap) {
kfree(mgs);
kvm->arch.migration_state = NULL;
return -ENOMEM;
}

mgs->bitmap_size = ram_pages;
atomic64_set(&mgs->dirty_pages, ram_pages);
/* mark all the pages in active slots as dirty */
for (slotnr = 0; slotnr < slots->used_slots; slotnr++) {
ms = slots->memslots + slotnr;
bitmap_set(mgs->pgste_bitmap, ms->base_gfn, ms->npages);
}

kvm_s390_sync_request_broadcast(kvm, KVM_REQ_START_MIGRATION);
memset(kvm_second_dirty_bitmap(ms), 0xff, kvm_dirty_bitmap_bytes(ms));
ram_pages += ms->npages;
}
atomic64_set(&kvm->arch.cmma_dirty_pages, ram_pages);
kvm->arch.migration_mode = 1;
kvm_s390_sync_request_broadcast(kvm, KVM_REQ_START_MIGRATION);
return 0;
}

Expand All @@ -919,21 +902,12 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm)
*/
static int kvm_s390_vm_stop_migration(struct kvm *kvm)
{
struct kvm_s390_migration_state *mgs;

/* migration mode already disabled */
if (!kvm->arch.migration_state)
if (!kvm->arch.migration_mode)
return 0;
mgs = kvm->arch.migration_state;
kvm->arch.migration_state = NULL;

if (kvm->arch.use_cmma) {
kvm->arch.migration_mode = 0;
if (kvm->arch.use_cmma)
kvm_s390_sync_request_broadcast(kvm, KVM_REQ_STOP_MIGRATION);
/* We have to wait for the essa emulation to finish */
synchronize_srcu(&kvm->srcu);
vfree(mgs->pgste_bitmap);
}
kfree(mgs);
return 0;
}

Expand Down Expand Up @@ -961,7 +935,7 @@ static int kvm_s390_vm_set_migration(struct kvm *kvm,
static int kvm_s390_vm_get_migration(struct kvm *kvm,
struct kvm_device_attr *attr)
{
u64 mig = (kvm->arch.migration_state != NULL);
u64 mig = kvm->arch.migration_mode;

if (attr->attr != KVM_S390_VM_MIGRATION_STATUS)
return -ENXIO;
Expand Down Expand Up @@ -1599,6 +1573,134 @@ static long kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
/* for consistency */
#define KVM_S390_CMMA_SIZE_MAX ((u32)KVM_S390_SKEYS_MAX)

/*
* Similar to gfn_to_memslot, but returns the index of a memslot also when the
* address falls in a hole. In that case the index of one of the memslots
* bordering the hole is returned.
*/
static int gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn)
{
int start = 0, end = slots->used_slots;
int slot = atomic_read(&slots->lru_slot);
struct kvm_memory_slot *memslots = slots->memslots;

if (gfn >= memslots[slot].base_gfn &&
gfn < memslots[slot].base_gfn + memslots[slot].npages)
return slot;

while (start < end) {
slot = start + (end - start) / 2;

if (gfn >= memslots[slot].base_gfn)
end = slot;
else
start = slot + 1;
}

if (gfn >= memslots[start].base_gfn &&
gfn < memslots[start].base_gfn + memslots[start].npages) {
atomic_set(&slots->lru_slot, start);
}

return start;
}

static int kvm_s390_peek_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
u8 *res, unsigned long bufsize)
{
unsigned long pgstev, hva, cur_gfn = args->start_gfn;

args->count = 0;
while (args->count < bufsize) {
hva = gfn_to_hva(kvm, cur_gfn);
/*
* We return an error if the first value was invalid, but we
* return successfully if at least one value was copied.
*/
if (kvm_is_error_hva(hva))
return args->count ? 0 : -EFAULT;
if (get_pgste(kvm->mm, hva, &pgstev) < 0)
pgstev = 0;
res[args->count++] = (pgstev >> 24) & 0x43;
cur_gfn++;
}

return 0;
}

static unsigned long kvm_s390_next_dirty_cmma(struct kvm_memslots *slots,
unsigned long cur_gfn)
{
int slotidx = gfn_to_memslot_approx(slots, cur_gfn);
struct kvm_memory_slot *ms = slots->memslots + slotidx;
unsigned long ofs = cur_gfn - ms->base_gfn;

if (ms->base_gfn + ms->npages <= cur_gfn) {
slotidx--;
/* If we are above the highest slot, wrap around */
if (slotidx < 0)
slotidx = slots->used_slots - 1;

ms = slots->memslots + slotidx;
ofs = 0;
}
ofs = find_next_bit(kvm_second_dirty_bitmap(ms), ms->npages, ofs);
while ((slotidx > 0) && (ofs >= ms->npages)) {
slotidx--;
ms = slots->memslots + slotidx;
ofs = find_next_bit(kvm_second_dirty_bitmap(ms), ms->npages, 0);
}
return ms->base_gfn + ofs;
}

static int kvm_s390_get_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
u8 *res, unsigned long bufsize)
{
unsigned long mem_end, cur_gfn, next_gfn, hva, pgstev;
struct kvm_memslots *slots = kvm_memslots(kvm);
struct kvm_memory_slot *ms;

cur_gfn = kvm_s390_next_dirty_cmma(slots, args->start_gfn);
ms = gfn_to_memslot(kvm, cur_gfn);
args->count = 0;
args->start_gfn = cur_gfn;
if (!ms)
return 0;
next_gfn = kvm_s390_next_dirty_cmma(slots, cur_gfn + 1);
mem_end = slots->memslots[0].base_gfn + slots->memslots[0].npages;

while (args->count < bufsize) {
hva = gfn_to_hva(kvm, cur_gfn);
if (kvm_is_error_hva(hva))
return 0;
/* Decrement only if we actually flipped the bit to 0 */
if (test_and_clear_bit(cur_gfn - ms->base_gfn, kvm_second_dirty_bitmap(ms)))
atomic64_dec(&kvm->arch.cmma_dirty_pages);
if (get_pgste(kvm->mm, hva, &pgstev) < 0)
pgstev = 0;
/* Save the value */
res[args->count++] = (pgstev >> 24) & 0x43;
/* If the next bit is too far away, stop. */
if (next_gfn > cur_gfn + KVM_S390_MAX_BIT_DISTANCE)
return 0;
/* If we reached the previous "next", find the next one */
if (cur_gfn == next_gfn)
next_gfn = kvm_s390_next_dirty_cmma(slots, cur_gfn + 1);
/* Reached the end of memory or of the buffer, stop */
if ((next_gfn >= mem_end) ||
(next_gfn - args->start_gfn >= bufsize))
return 0;
cur_gfn++;
/* Reached the end of the current memslot, take the next one. */
if (cur_gfn - ms->base_gfn >= ms->npages) {
ms = gfn_to_memslot(kvm, cur_gfn);
if (!ms)
return 0;
}
}
return 0;
}

/*
* This function searches for the next page with dirty CMMA attributes, and
* saves the attributes in the buffer up to either the end of the buffer or
Expand All @@ -1610,97 +1712,54 @@ static long kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
static int kvm_s390_get_cmma_bits(struct kvm *kvm,
struct kvm_s390_cmma_log *args)
{
struct kvm_s390_migration_state *s = kvm->arch.migration_state;
unsigned long bufsize, hva, pgstev, i, next, cur;
int srcu_idx, peek, r = 0, rr;
u8 *res;

cur = args->start_gfn;
i = next = pgstev = 0;
unsigned long bufsize;
int srcu_idx, peek, ret;
u8 *values;

if (unlikely(!kvm->arch.use_cmma))
if (!kvm->arch.use_cmma)
return -ENXIO;
/* Invalid/unsupported flags were specified */
if (args->flags & ~KVM_S390_CMMA_PEEK)
return -EINVAL;
/* Migration mode query, and we are not doing a migration */
peek = !!(args->flags & KVM_S390_CMMA_PEEK);
if (!peek && !s)
if (!peek && !kvm->arch.migration_mode)
return -EINVAL;
/* CMMA is disabled or was not used, or the buffer has length zero */
bufsize = min(args->count, KVM_S390_CMMA_SIZE_MAX);
if (!bufsize || !kvm->mm->context.uses_cmm) {
memset(args, 0, sizeof(*args));
return 0;
}

if (!peek) {
/* We are not peeking, and there are no dirty pages */
if (!atomic64_read(&s->dirty_pages)) {
memset(args, 0, sizeof(*args));
return 0;
}
cur = find_next_bit(s->pgste_bitmap, s->bitmap_size,
args->start_gfn);
if (cur >= s->bitmap_size) /* nothing found, loop back */
cur = find_next_bit(s->pgste_bitmap, s->bitmap_size, 0);
if (cur >= s->bitmap_size) { /* again! (very unlikely) */
memset(args, 0, sizeof(*args));
return 0;
}
next = find_next_bit(s->pgste_bitmap, s->bitmap_size, cur + 1);
/* We are not peeking, and there are no dirty pages */
if (!peek && !atomic64_read(&kvm->arch.cmma_dirty_pages)) {
memset(args, 0, sizeof(*args));
return 0;
}

res = vmalloc(bufsize);
if (!res)
values = vmalloc(bufsize);
if (!values)
return -ENOMEM;

args->start_gfn = cur;

down_read(&kvm->mm->mmap_sem);
srcu_idx = srcu_read_lock(&kvm->srcu);
while (i < bufsize) {
hva = gfn_to_hva(kvm, cur);
if (kvm_is_error_hva(hva)) {
r = -EFAULT;
break;
}
/* decrement only if we actually flipped the bit to 0 */
if (!peek && test_and_clear_bit(cur, s->pgste_bitmap))
atomic64_dec(&s->dirty_pages);
r = get_pgste(kvm->mm, hva, &pgstev);
if (r < 0)
pgstev = 0;
/* save the value */
res[i++] = (pgstev >> 24) & 0x43;
/*
* if the next bit is too far away, stop.
* if we reached the previous "next", find the next one
*/
if (!peek) {
if (next > cur + KVM_S390_MAX_BIT_DISTANCE)
break;
if (cur == next)
next = find_next_bit(s->pgste_bitmap,
s->bitmap_size, cur + 1);
/* reached the end of the bitmap or of the buffer, stop */
if ((next >= s->bitmap_size) ||
(next >= args->start_gfn + bufsize))
break;
}
cur++;
}
if (peek)
ret = kvm_s390_peek_cmma(kvm, args, values, bufsize);
else
ret = kvm_s390_get_cmma(kvm, args, values, bufsize);
srcu_read_unlock(&kvm->srcu, srcu_idx);
up_read(&kvm->mm->mmap_sem);
args->count = i;
args->remaining = s ? atomic64_read(&s->dirty_pages) : 0;

rr = copy_to_user((void __user *)args->values, res, args->count);
if (rr)
r = -EFAULT;
if (kvm->arch.migration_mode)
args->remaining = atomic64_read(&kvm->arch.cmma_dirty_pages);
else
args->remaining = 0;

vfree(res);
return r;
if (copy_to_user((void __user *)args->values, values, args->count))
ret = -EFAULT;

vfree(values);
return ret;
}

/*
Expand Down Expand Up @@ -2139,10 +2198,6 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
kvm_s390_destroy_adapters(kvm);
kvm_s390_clear_float_irqs(kvm);
kvm_s390_vsie_destroy(kvm);
if (kvm->arch.migration_state) {
vfree(kvm->arch.migration_state->pgste_bitmap);
kfree(kvm->arch.migration_state);
}
KVM_EVENT(3, "vm 0x%pK destroyed", kvm);
}

Expand Down
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