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KVM: s390: ioctls to get and set guest storage attributes
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* Add the struct used in the ioctls to get and set CMMA attributes.
* Add the two functions needed to get and set the CMMA attributes for
  guest pages.
* Add the two ioctls that use the aforementioned functions.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
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Claudio Imbrenda authored and Christian Borntraeger committed Jun 22, 2017
1 parent 190df4a commit 4036e38
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135 changes: 135 additions & 0 deletions Documentation/virtual/kvm/api.txt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3255,6 +3255,141 @@ Otherwise, if the MCE is a corrected error, KVM will just
store it in the corresponding bank (provided this bank is
not holding a previously reported uncorrected error).

4.107 KVM_S390_GET_CMMA_BITS

Capability: KVM_CAP_S390_CMMA_MIGRATION
Architectures: s390
Type: vm ioctl
Parameters: struct kvm_s390_cmma_log (in, out)
Returns: 0 on success, a negative value on error

This ioctl is used to get the values of the CMMA bits on the s390
architecture. It is meant to be used in two scenarios:
- During live migration to save the CMMA values. Live migration needs
to be enabled via the KVM_REQ_START_MIGRATION VM property.
- To non-destructively peek at the CMMA values, with the flag
KVM_S390_CMMA_PEEK set.

The ioctl takes parameters via the kvm_s390_cmma_log struct. The desired
values are written to a buffer whose location is indicated via the "values"
member in the kvm_s390_cmma_log struct. The values in the input struct are
also updated as needed.
Each CMMA value takes up one byte.

struct kvm_s390_cmma_log {
__u64 start_gfn;
__u32 count;
__u32 flags;
union {
__u64 remaining;
__u64 mask;
};
__u64 values;
};

start_gfn is the number of the first guest frame whose CMMA values are
to be retrieved,

count is the length of the buffer in bytes,

values points to the buffer where the result will be written to.

If count is greater than KVM_S390_SKEYS_MAX, then it is considered to be
KVM_S390_SKEYS_MAX. KVM_S390_SKEYS_MAX is re-used for consistency with
other ioctls.

The result is written in the buffer pointed to by the field values, and
the values of the input parameter are updated as follows.

Depending on the flags, different actions are performed. The only
supported flag so far is KVM_S390_CMMA_PEEK.

The default behaviour if KVM_S390_CMMA_PEEK is not set is:
start_gfn will indicate the first page frame whose CMMA bits were dirty.
It is not necessarily the same as the one passed as input, as clean pages
are skipped.

count will indicate the number of bytes actually written in the buffer.
It can (and very often will) be smaller than the input value, since the
buffer is only filled until 16 bytes of clean values are found (which
are then not copied in the buffer). Since a CMMA migration block needs
the base address and the length, for a total of 16 bytes, we will send
back some clean data if there is some dirty data afterwards, as long as
the size of the clean data does not exceed the size of the header. This
allows to minimize the amount of data to be saved or transferred over
the network at the expense of more roundtrips to userspace. The next
invocation of the ioctl will skip over all the clean values, saving
potentially more than just the 16 bytes we found.

If KVM_S390_CMMA_PEEK is set:
the existing storage attributes are read even when not in migration
mode, and no other action is performed;

the output start_gfn will be equal to the input start_gfn,

the output count will be equal to the input count, except if the end of
memory has been reached.

In both cases:
the field "remaining" will indicate the total number of dirty CMMA values
still remaining, or 0 if KVM_S390_CMMA_PEEK is set and migration mode is
not enabled.

mask is unused.

values points to the userspace buffer where the result will be stored.

This ioctl can fail with -ENOMEM if not enough memory can be allocated to
complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if
KVM_S390_CMMA_PEEK is not set but migration mode was not enabled, with
-EFAULT if the userspace address is invalid or if no page table is
present for the addresses (e.g. when using hugepages).

4.108 KVM_S390_SET_CMMA_BITS

Capability: KVM_CAP_S390_CMMA_MIGRATION
Architectures: s390
Type: vm ioctl
Parameters: struct kvm_s390_cmma_log (in)
Returns: 0 on success, a negative value on error

This ioctl is used to set the values of the CMMA bits on the s390
architecture. It is meant to be used during live migration to restore
the CMMA values, but there are no restrictions on its use.
The ioctl takes parameters via the kvm_s390_cmma_values struct.
Each CMMA value takes up one byte.

struct kvm_s390_cmma_log {
__u64 start_gfn;
__u32 count;
__u32 flags;
union {
__u64 remaining;
__u64 mask;
};
__u64 values;
};

start_gfn indicates the starting guest frame number,

count indicates how many values are to be considered in the buffer,

flags is not used and must be 0.

mask indicates which PGSTE bits are to be considered.

remaining is not used.

values points to the buffer in userspace where to store the values.

This ioctl can fail with -ENOMEM if not enough memory can be allocated to
complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if
the count field is too large (e.g. more than KVM_S390_CMMA_SIZE_MAX) or
if the flags field was not 0, with -EFAULT if the userspace address is
invalid, if invalid pages are written to (e.g. after the end of memory)
or if no page table is present for the addresses (e.g. when using
hugepages).

5. The kvm_run structure
------------------------

Expand Down
202 changes: 201 additions & 1 deletion arch/s390/kvm/kvm-s390.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -30,8 +30,8 @@
#include <linux/vmalloc.h>
#include <linux/bitmap.h>
#include <linux/sched/signal.h>

#include <linux/string.h>

#include <asm/asm-offsets.h>
#include <asm/lowcore.h>
#include <asm/stp.h>
Expand Down Expand Up @@ -387,6 +387,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_S390_SKEYS:
case KVM_CAP_S390_IRQ_STATE:
case KVM_CAP_S390_USER_INSTR0:
case KVM_CAP_S390_CMMA_MIGRATION:
case KVM_CAP_S390_AIS:
r = 1;
break;
Expand Down Expand Up @@ -1419,6 +1420,182 @@ static long kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
return r;
}

/*
* Base address and length must be sent at the start of each block, therefore
* it's cheaper to send some clean data, as long as it's less than the size of
* two longs.
*/
#define KVM_S390_MAX_BIT_DISTANCE (2 * sizeof(void *))
/* for consistency */
#define KVM_S390_CMMA_SIZE_MAX ((u32)KVM_S390_SKEYS_MAX)

/*
* 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
* until a block of at least KVM_S390_MAX_BIT_DISTANCE clean bits is found;
* no trailing clean bytes are saved.
* In case no dirty bits were found, or if CMMA was not enabled or used, the
* output buffer will indicate 0 as length.
*/
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;

if (unlikely(!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)
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.use_cmma) {
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);
}

res = vmalloc(bufsize);
if (!res)
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) & 0x3;
/*
* 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++;
}
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;

vfree(res);
return r;
}

/*
* This function sets the CMMA attributes for the given pages. If the input
* buffer has zero length, no action is taken, otherwise the attributes are
* set and the mm->context.use_cmma flag is set.
*/
static int kvm_s390_set_cmma_bits(struct kvm *kvm,
const struct kvm_s390_cmma_log *args)
{
unsigned long hva, mask, pgstev, i;
uint8_t *bits;
int srcu_idx, r = 0;

mask = args->mask;

if (!kvm->arch.use_cmma)
return -ENXIO;
/* invalid/unsupported flags */
if (args->flags != 0)
return -EINVAL;
/* Enforce sane limit on memory allocation */
if (args->count > KVM_S390_CMMA_SIZE_MAX)
return -EINVAL;
/* Nothing to do */
if (args->count == 0)
return 0;

bits = vmalloc(sizeof(*bits) * args->count);
if (!bits)
return -ENOMEM;

r = copy_from_user(bits, (void __user *)args->values, args->count);
if (r) {
r = -EFAULT;
goto out;
}

down_read(&kvm->mm->mmap_sem);
srcu_idx = srcu_read_lock(&kvm->srcu);
for (i = 0; i < args->count; i++) {
hva = gfn_to_hva(kvm, args->start_gfn + i);
if (kvm_is_error_hva(hva)) {
r = -EFAULT;
break;
}

pgstev = bits[i];
pgstev = pgstev << 24;
mask &= _PGSTE_GPS_USAGE_MASK;
set_pgste_bits(kvm->mm, hva, mask, pgstev);
}
srcu_read_unlock(&kvm->srcu, srcu_idx);
up_read(&kvm->mm->mmap_sem);

if (!kvm->mm->context.use_cmma) {
down_write(&kvm->mm->mmap_sem);
kvm->mm->context.use_cmma = 1;
up_write(&kvm->mm->mmap_sem);
}
out:
vfree(bits);
return r;
}

long kvm_arch_vm_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
{
Expand Down Expand Up @@ -1497,6 +1674,29 @@ long kvm_arch_vm_ioctl(struct file *filp,
r = kvm_s390_set_skeys(kvm, &args);
break;
}
case KVM_S390_GET_CMMA_BITS: {
struct kvm_s390_cmma_log args;

r = -EFAULT;
if (copy_from_user(&args, argp, sizeof(args)))
break;
r = kvm_s390_get_cmma_bits(kvm, &args);
if (!r) {
r = copy_to_user(argp, &args, sizeof(args));
if (r)
r = -EFAULT;
}
break;
}
case KVM_S390_SET_CMMA_BITS: {
struct kvm_s390_cmma_log args;

r = -EFAULT;
if (copy_from_user(&args, argp, sizeof(args)))
break;
r = kvm_s390_set_cmma_bits(kvm, &args);
break;
}
default:
r = -ENOTTY;
}
Expand Down
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