From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43015) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dAZmp-0000bA-LV for qemu-devel@nongnu.org; Tue, 16 May 2017 06:33:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dAZml-0002xF-JF for qemu-devel@nongnu.org; Tue, 16 May 2017 06:33:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36522) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dAZml-0002wL-Ab for qemu-devel@nongnu.org; Tue, 16 May 2017 06:32:59 -0400 Date: Tue, 16 May 2017 11:32:51 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170516103250.GB2839@work-vm> References: <1494595886-30912-1-git-send-email-a.perevalov@samsung.com> <1494595886-30912-5-git-send-email-a.perevalov@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1494595886-30912-5-git-send-email-a.perevalov@samsung.com> Subject: Re: [Qemu-devel] [PATCH V5 4/9] migration: split ufd_version_check onto receive/request features part List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Perevalov Cc: qemu-devel@nongnu.org, i.maximets@samsung.com, peterx@redhat.com * Alexey Perevalov (a.perevalov@samsung.com) 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 > --- > 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 > #include > > -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 > + */ > +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 / dgilbert@redhat.com / Manchester, UK