Re: [Qemu-devel] [PATCH qemu v5 06/12] vfio: spapr: Add SPAPR IOMMU v2 support (DMA memory preregistering)

[Alexey Kardashevskiy]

On 04/08/2015 12:15 PM, David Gibson wrote:
> On Tue, Mar 31, 2015 at 04:28:41PM +1100, Alexey Kardashevskiy wrote:
> > This makes use of the new "memory registering" feature. The idea is
> > to provide the guest ability to notify the host kernel about pages which
>
> AFAICT it's not really the guest informing the host, just qemu
> informing the host.  If I'm reading the code correctly, qemu registers
> all RAM regionns, without guest intervention.

Right. Wrong commit log, I'll fix it.


> > are going to be used for DMA. Having this information, the host kernel
> > can pin them all once per user process, do locked pages accounting (once)
> > and not spent time on doing that in real time with possible failures
> > which cannot be handled nicely in some cases.
> >
> > This adds a guest RAM memory listener which notifies a VFIO container
> > about memory which needs to be pinned/unpinned. VFIO MMIO regions
> > (i.e. "skip dump" regions) are skipped.
> >
> > The feature is only enabled for SPAPR IOMMU v2. The host kernel changes
> > are required. Since v2 does not need/support VFIO_IOMMU_ENABLE, this does
> > not call it when v2 is detected and enabled.
>
> So I'm clear, the v2 just represents a new userspace<->host kernel
> interface for controlling the IOMMU, doesn't it?  It doesn't change
> the guest visible IOMMU interface and doesn't represent different
> IOMMU hardware?


Exactly true.


> > Signed-off-by: Alexey Kardashevskiy <address@hidden>
> > ---
> > Changes:
> > v5:
> > * simplified the patch
> > * added trace points
> > * added round_up() for the size
> > * SPAPR IOMMU v2 used
> > ---
> >   hw/vfio/common.c              | 26 +++++++++-----
> >   hw/vfio/spapr.c               | 79 +++++++++++++++++++++++++++++++++++++++++--
> >   include/hw/vfio/vfio-common.h |  5 ++-
> >   trace-events                  |  1 +
> >   4 files changed, 100 insertions(+), 11 deletions(-)
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index a71f881..e35e478 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -577,14 +577,18 @@ static int vfio_connect_container(VFIOGroup *group, 
> > AddressSpace *as)
> >
> >           container->iommu_data.type1.initialized = true;
> >
> > -    } else if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU)) {
> > +    } else if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU) ||
> > +               ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_v2_IOMMU)) {
> > +        bool v2 = !!ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_v2_IOMMU);
> > +
> >           ret = ioctl(group->fd, VFIO_GROUP_SET_CONTAINER, &fd);
> >           if (ret) {
> >               error_report("vfio: failed to set group container: %m");
> >               ret = -errno;
> >               goto free_container_exit;
> >           }
> > -        ret = ioctl(fd, VFIO_SET_IOMMU, VFIO_SPAPR_TCE_IOMMU);
> > +        ret = ioctl(fd, VFIO_SET_IOMMU,
> > +                v2 ? VFIO_SPAPR_TCE_v2_IOMMU : VFIO_SPAPR_TCE_IOMMU);
> >           if (ret) {
> >               error_report("vfio: failed to set iommu for container: %m");
> >               ret = -errno;
> > @@ -596,14 +600,20 @@ static int vfio_connect_container(VFIOGroup *group, 
> > AddressSpace *as)
> >            * when container fd is closed so we do not call it explicitly
> >            * in this file.
> >            */
> > -        ret = ioctl(fd, VFIO_IOMMU_ENABLE);
> > -        if (ret) {
> > -            error_report("vfio: failed to enable container: %m");
> > -            ret = -errno;
> > -            goto free_container_exit;
> > +        if (!v2) {
> > +            ret = ioctl(fd, VFIO_IOMMU_ENABLE);
> > +            if (ret) {
> > +                error_report("vfio: failed to enable container: %m");
> > +                ret = -errno;
> > +                goto free_container_exit;
> > +            }
> >           }
> >
> > -        spapr_memory_listener_register(container);
> > +        ret = spapr_memory_listener_register(container, v2 ? 2 : 1);
> > +        if (ret) {
> > +            error_report("vfio: RAM memory listener initialization failed for 
> > container");
> > +            goto listener_release_exit;
> > +        }
> >
> >       } else {
> >           error_report("vfio: No available IOMMU models");
> > diff --git a/hw/vfio/spapr.c b/hw/vfio/spapr.c
> > index 5f79194..a670907 100644
> > --- a/hw/vfio/spapr.c
> > +++ b/hw/vfio/spapr.c
> > @@ -17,6 +17,9 @@
> >    *  along with this program; if not, see <http://www.gnu.org/licenses/>.
> >    */
> >
> > +#include <sys/ioctl.h>
> > +#include <linux/vfio.h>
> > +
> >   #include "hw/vfio/vfio-common.h"
> >   #include "qemu/error-report.h"
> >   #include "trace.h"
> > @@ -211,16 +214,88 @@ static const MemoryListener vfio_spapr_memory_listener = {
> >       .region_del = vfio_spapr_listener_region_del,
> >   };
> >
> > +static void vfio_ram_do_region(VFIOContainer *container,
> > +                              MemoryRegionSection *section, unsigned long req)
> > +{
> > +    int ret;
> > +    struct vfio_iommu_spapr_register_memory reg = { .argsz = sizeof(reg) };
> > +
> > +    if (!memory_region_is_ram(section->mr) ||
> > +        memory_region_is_skip_dump(section->mr)) {
> > +        return;
> > +    }
> > +
> > +    reg.vaddr = (__u64) memory_region_get_ram_ptr(section->mr) +
> > +        section->offset_within_region;
>
> Is section->offset_within_region always page aligned?


I think so as it is RAM. qemu_ram_alloc_from_file() and 
qemu_ram_alloc_internal() (called from memory_region_init_ram()) align.


> > +    reg.size = ROUND_UP(int128_get64(section->size), TARGET_PAGE_SIZE);
> > +
> > +    ret = ioctl(container->fd, req, &reg);
> > +    trace_vfio_ram_register(_IOC_NR(req) - VFIO_BASE, reg.vaddr, reg.size, 
> > ret);
> > +
> > +    /*
> > +     * On the initfn path, store the first error in the container so we
> > +     * can gracefully fail.  Runtime, there's not much we can do other
> > +     * than throw a hardware error.
> > +     */
> > +    if (!container->iommu_data.spapr.ram_reg_initialized) {
> > +        if (!container->iommu_data.spapr.ram_reg_error) {
> > +            container->iommu_data.spapr.ram_reg_error = ret;
> > +        }
>
> This is pretty clunky, but I don't immediately see a better way.
>
> Also.. won't the return value of ioctl() just be -1 on error, which
> won't tell you much.  Do you want to store errno, instead?

Yes, I do, I'll fix it. Thanks.


> > +    } else {
> > +        hw_error("vfio: RAM registering failed, unable to continue");
> > +    }
> > +}
> > +
> > +static void vfio_spapr_ram_listener_region_add(MemoryListener *listener,
> > +                                               MemoryRegionSection *section)
> > +{
> > +    VFIOContainer *container = container_of(listener, VFIOContainer,
> > +                                            iommu_data.spapr.ramlistener);
> > +    memory_region_ref(section->mr);
> > +    vfio_ram_do_region(container, section, VFIO_IOMMU_SPAPR_REGISTER_MEMORY);
> > +}
> > +
> > +static void vfio_spapr_ram_listener_region_del(MemoryListener *listener,
> > +                                               MemoryRegionSection *section)
> > +{
> > +    VFIOContainer *container = container_of(listener, VFIOContainer,
> > +                                            iommu_data.spapr.ramlistener);
> > +    memory_region_unref(section->mr);
> > +    vfio_ram_do_region(container, section, VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY);
> > +}
> > +
> > +static const MemoryListener vfio_spapr_ram_memory_listener = {
> > +    .region_add = vfio_spapr_ram_listener_region_add,
> > +    .region_del = vfio_spapr_ram_listener_region_del,
> > +};
> > +
> >   static void vfio_spapr_listener_release(VFIOContainer *container)
> >   {
> >       memory_listener_unregister(&container->iommu_data.spapr.listener);
> >   }
> >
> > -void spapr_memory_listener_register(VFIOContainer *container)
> > +static void vfio_spapr_listener_release_v2(VFIOContainer *container)
> > +{
> > +    memory_listener_unregister(&container->iommu_data.spapr.listener);
> > +    vfio_spapr_listener_release(container);
> > +}
> > +
> > +int spapr_memory_listener_register(VFIOContainer *container, int ver)
> >   {
> >       container->iommu_data.spapr.listener = vfio_spapr_memory_listener;
> >       container->iommu_data.release = vfio_spapr_listener_release;
> > -
> >       memory_listener_register(&container->iommu_data.spapr.listener,
> >                                container->space->as);
> > +    if (ver < 2) {
> > +        return 0;
> > +    }
> > +
> > +    container->iommu_data.spapr.ramlistener = vfio_spapr_ram_memory_listener;
> > +    container->iommu_data.release = vfio_spapr_listener_release_v2;
> > +    memory_listener_register(&container->iommu_data.spapr.ramlistener,
> > +                             &address_space_memory);
> > +
> > +    container->iommu_data.spapr.ram_reg_initialized = true;
> > +
> > +    return container->iommu_data.spapr.ram_reg_error;
> >   }
> > diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> > index d0b831c..b5ef446 100644
> > --- a/include/hw/vfio/vfio-common.h
> > +++ b/include/hw/vfio/vfio-common.h
> > @@ -71,6 +71,9 @@ typedef struct VFIOType1 {
> >
> >   typedef struct VFIOSPAPR {
> >       MemoryListener listener;
> > +    MemoryListener ramlistener;
> > +    int ram_reg_error;
> > +    bool ram_reg_initialized;
> >   } VFIOSPAPR;
> >
> >   typedef struct VFIOContainer {
> > @@ -156,6 +159,6 @@ extern int vfio_dma_unmap(VFIOContainer *container,
> >                             hwaddr iova, ram_addr_t size);
> >   bool vfio_listener_skipped_section(MemoryRegionSection *section);
> >
> > -extern void spapr_memory_listener_register(VFIOContainer *container);
> > +extern int spapr_memory_listener_register(VFIOContainer *container, int ver);
> >
> >   #endif /* !HW_VFIO_VFIO_COMMON_H */
> > diff --git a/trace-events b/trace-events
> > index 1231ba4..2739140 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1563,6 +1563,7 @@ vfio_disconnect_container(int fd) "close container->fd=%d"
> >   vfio_put_group(int fd) "close group->fd=%d"
> >   vfio_get_device(const char * name, unsigned int flags, unsigned int num_regions, 
> > unsigned int num_irqs) "Device %s flags: %u, regions: %u, irqs: %u"
> >   vfio_put_base_device(int fd) "close vdev->fd=%d"
> > +vfio_ram_register(int req, uint64_t va, uint64_t size, int ret) "req=%d va=%"PRIx64" 
> > size=%"PRIx64" ret=%d"
> >
> >   #hw/acpi/memory_hotplug.c
> >   mhp_acpi_invalid_slot_selected(uint32_t slot) "0x%"PRIx32


--
Alexey