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Re: [Qemu-devel] [PATCH V5 4/9] migration: split ufd_version_check onto
From: |
Alexey |
Subject: |
Re: [Qemu-devel] [PATCH V5 4/9] migration: split ufd_version_check onto receive/request features part |
Date: |
Thu, 18 May 2017 09:55:18 +0300 |
User-agent: |
Mutt/1.7.2+51 (519a8c8cc55c) (2016-11-26) |
On Tue, May 16, 2017 at 11:32:51AM +0100, Dr. David Alan Gilbert wrote:
> * Alexey Perevalov (address@hidden) wrote:
> > This modification is necessary for userfault fd features which are
> > required to be requested from userspace.
> > UFFD_FEATURE_THREAD_ID is a one of such "on demand" feature, which will
> > be introduced in the next patch.
> >
> > QEMU need to use separate userfault file descriptor, due to
> > userfault context has internal state, and after first call of
> > ioctl UFFD_API it changes its state to UFFD_STATE_RUNNING (in case of
> > success), but
> > kernel while handling ioctl UFFD_API expects UFFD_STATE_WAIT_API. So
> > only one ioctl with UFFD_API is possible per ufd.
> >
> > Signed-off-by: Alexey Perevalov <address@hidden>
> > ---
> > migration/postcopy-ram.c | 82
> > ++++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 73 insertions(+), 9 deletions(-)
> >
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index 0f75700..c96d5f5 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -60,32 +60,96 @@ struct PostcopyDiscardState {
> > #include <sys/eventfd.h>
> > #include <linux/userfaultfd.h>
> >
> > -static bool ufd_version_check(int ufd, MigrationIncomingState *mis)
> > +
> > +/*
> > + * Check userfault fd features, to request only supported features in
> > + * future.
> > + * __NR_userfaultfd - should be checked before
> > + * Return obtained features
>
> That's not quite right;
> * Returns: True on success, sets *features to supported features
> False on failure or if kernel doesn't support ufd
>
yes, obtained features is out parameter,
but I want to keep false uncommented and just add error_report into
syscall check, because the possible reason of failure is:
1. No syscall userfaultfd, but function expects that syscall, it reflects in
comment
2 Within syscall: exhausted fd or out of memory (file in kernel
is allocating)
3. Problem in ioctl due to internal state of UFFD, as example
UFFDIO_API after UFFDIO_REGISTER
Also I would prefer follow migration/ram.c comment style.
> > + */
> > +static bool receive_ufd_features(uint64_t *features)
> > {
> > - struct uffdio_api api_struct;
> > - uint64_t ioctl_mask;
> > + struct uffdio_api api_struct = {0};
> > + int ufd;
> > + bool ret = true;
> > +
> > + /* if we are here __NR_userfaultfd should exists */
> > + ufd = syscall(__NR_userfaultfd, O_CLOEXEC);
> > + if (ufd == -1) {
> > + return false;
> > + }
> >
> > + /* ask features */
> > api_struct.api = UFFD_API;
> > api_struct.features = 0;
> > if (ioctl(ufd, UFFDIO_API, &api_struct)) {
> > - error_report("%s: UFFDIO_API failed: %s", __func__
> > + error_report("%s: UFFDIO_API failed: %s", __func__,
> > strerror(errno));
> > + ret = false;
> > + goto release_ufd;
> > + }
> > +
> > + *features = api_struct.features;
> > +
> > +release_ufd:
> > + close(ufd);
> > + return ret;
> > +}
>
> Needs a comment; perhaps something like:
> * Called once on a newly opened ufd, can request specific features.
> * Returns: True on success
>
> > +static bool request_ufd_features(int ufd, uint64_t features)
> > +{
> > + struct uffdio_api api_struct = {0};
> > + uint64_t ioctl_mask;
> > +
> > + api_struct.api = UFFD_API;
> > + api_struct.features = features;
> > + if (ioctl(ufd, UFFDIO_API, &api_struct)) {
> > + error_report("%s failed: UFFDIO_API failed: %s", __func__,
> > + strerror(errno));
> > return false;
> > }
> >
> > - ioctl_mask = (__u64)1 << _UFFDIO_REGISTER |
> > - (__u64)1 << _UFFDIO_UNREGISTER;
> > + ioctl_mask = 1 << _UFFDIO_REGISTER |
> > + 1 << _UFFDIO_UNREGISTER;
> > if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
> > error_report("Missing userfault features: %" PRIx64,
> > (uint64_t)(~api_struct.ioctls & ioctl_mask));
> > return false;
> > }
> >
> > + return true;
> > +}
> > +
> > +static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis)
> > +{
> > + uint64_t asked_features = 0;
> > + uint64_t supported_features;
> > +
> > + /*
> > + * it's not possible to
> > + * request UFFD_API twice per one fd
> > + */
> > + if (!receive_ufd_features(&supported_features)) {
> > + error_report("%s failed", __func__);
> > + return false;
> > + }
> > +
> > + /*
> > + * request features, even if asked_features is 0, due to
> > + * kernel expects UFFD_API before UFFDIO_REGISTER, per
> > + * userfault file descriptor
> > + */
> > + if (!request_ufd_features(ufd, asked_features)) {
> > + error_report("%s failed: features %" PRIu64, __func__,
> > + asked_features);
> > + return false;
> > + }
> > +
> > if (getpagesize() != ram_pagesize_summary()) {
> > bool have_hp = false;
> > /* We've got a huge page */
> > #ifdef UFFD_FEATURE_MISSING_HUGETLBFS
> > - have_hp = api_struct.features & UFFD_FEATURE_MISSING_HUGETLBFS;
> > + have_hp = supported_features & UFFD_FEATURE_MISSING_HUGETLBFS;
> > #endif
> > if (!have_hp) {
> > error_report("Userfault on this host does not support huge
> > pages");
> > @@ -136,7 +200,7 @@ bool
> > postcopy_ram_supported_by_host(MigrationIncomingState *mis)
> > }
> >
> > /* Version and features check */
> > - if (!ufd_version_check(ufd, mis)) {
> > + if (!ufd_check_and_apply(ufd, mis)) {
> > goto out;
> > }
> >
> > @@ -513,7 +577,7 @@ int postcopy_ram_enable_notify(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_version_check(mis->userfault_fd, mis)) {
> > + if (!ufd_check_and_apply(mis->userfault_fd, mis)) {
> > return -1;
> > }
> >
> > --
> > 1.9.1
>
> Dave
>
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>
--
BR
Alexey
- Re: [Qemu-devel] [PATCH V5 5/9] migration: introduce postcopy-blocktime capability, (continued)
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Re: [Qemu-devel] [PATCH V5 0/9] calculate blocktime for postcopy live migration, Eric Blake, 2017/05/12