[GIT PULL 2/9] KVM: s390: ioctls to get and set guest storage attributes

Christian Borntraeger
2017-06-28T17:30:37Z

From: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>

* 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>
---
Documentation/virtual/kvm/api.txt | 135 +++++++++++++++++++++++++
arch/s390/kvm/kvm-s390.c | 202 +++++++++++++++++++++++++++++++++++++-
include/uapi/linux/kvm.h | 33 +++++++
3 files changed, 369 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 4029943..912b7df 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -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
------------------------

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c2b3914..e100a7f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -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>
@@ -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;
@@ -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)
{
@@ -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;
}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 577429a..2b8dc1c 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -155,6 +155,35 @@ struct kvm_s390_skeys {
__u32 reserved[9];
};

+#define KVM_S390_CMMA_PEEK (1 << 0)
+
+/**
+ * kvm_s390_cmma_log - Used for CMMA migration.
+ *
+ * Used both for input and output.
+ *
+ * @start_gfn: Guest page number to start from.
+ * @count: Size of the result buffer.
+ * @flags: Control operation mode via KVM_S390_CMMA_* flags
+ * @remaining: Used with KVM_S390_GET_CMMA_BITS. Indicates how many dirty
+ * pages are still remaining.
+ * @mask: Used with KVM_S390_SET_CMMA_BITS. Bitmap of bits to actually set
+ * in the PGSTE.
+ * @values: Pointer to the values buffer.
+ *
+ * Used in KVM_S390_{G,S}ET_CMMA_BITS ioctls.
+ */
+struct kvm_s390_cmma_log {
+ __u64 start_gfn;
+ __u32 count;
+ __u32 flags;
+ union {
+ __u64 remaining;
+ __u64 mask;
+ };
+ __u64 values;
+};
+
struct kvm_hyperv_exit {
#define KVM_EXIT_HYPERV_SYNIC 1
#define KVM_EXIT_HYPERV_HCALL 2
@@ -895,6 +924,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_SPAPR_TCE_VFIO 142
#define KVM_CAP_X86_GUEST_MWAIT 143
#define KVM_CAP_ARM_USER_IRQ 144
+#define KVM_CAP_S390_CMMA_MIGRATION 145

#ifdef KVM_CAP_IRQ_ROUTING

@@ -1318,6 +1348,9 @@ struct kvm_s390_ucas_mapping {
#define KVM_S390_GET_IRQ_STATE _IOW(KVMIO, 0xb6, struct kvm_s390_irq_state)
/* Available with KVM_CAP_X86_SMM */
#define KVM_SMI _IO(KVMIO, 0xb7)
+/* Available with KVM_CAP_S390_CMMA_MIGRATION */
+#define KVM_S390_GET_CMMA_BITS _IOW(KVMIO, 0xb8, struct kvm_s390_cmma_log)
+#define KVM_S390_SET_CMMA_BITS _IOW(KVMIO, 0xb9, struct kvm_s390_cmma_log)

#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
--
2.7.4