Re: [Qemu-devel] [PATCH v4 2/2] qdisk - hw/block/xen_disk: grant copy implementation

[Paulina Szubarczyk <paulinaszubarczyk@gmail.com>]

On 08/08/2016 01:11 PM, Roger Pau Monné wrote:
> On Tue, Aug 02, 2016 at 04:06:30PM +0200, Paulina Szubarczyk wrote:
>> Copy data operated on during request from/to local buffers to/from
>> the grant references.
>>
>> Before grant copy operation local buffers must be allocated what is
>> done by calling ioreq_init_copy_buffers. For the 'read' operation,
>> first, the qemu device invokes the read operation on local buffers
>> and on the completion grant copy is called and buffers are freed.
>> For the 'write' operation grant copy is performed before invoking
>> write by qemu device.
>>
>> A new value 'feature_grant_copy' is added to recognize when the
>> grant copy operation is supported by a guest.
>>
>> Signed-off-by: Paulina Szubarczyk <paulinaszubarczyk@gmail.com>
>
> Thanks, this is looking good, just a couple of minor comments below.
>

Thank you for the review, I will apply the comments.

>> ---
>> Changes since v3:
>> - qemu_memalign/qemu_free is used instead function allocating
>>    memory from xc.
>> - removed the get_buffer function instead there is a direct call
>>    to qemu_memalign.
>> - moved ioreq_copy for write operation to ioreq_runio_qemu_aio.
>> - added struct xengnttab_grant_copy_segment_t and stub in
>>    xen_common.h for version of xen earlier then 480.
>> - added checking for version 480 to configure. The test repeats
>>    all the operation that are required for version < 480 and
>>    checks if xengnttab_grant_copy() is implemented.
>>
>> * I did not change the way of testing if grant_copy operation is
>>    implemented. As far as I understand if the code from
>>    gnttab_unimp.c is used then the gnttab device is unavailable
>>    and the handler to gntdev would be invalid. But if the handler
>>    is valid then the ioctl should return operation unimplemented
>>    if the gntdev does not implement the operation.
>> ---
>>   configure                   |  56 +++++++++++++++++
>>   hw/block/xen_disk.c         | 142 ++++++++++++++++++++++++++++++++++++++++++--
>>   include/hw/xen/xen_common.h |  25 ++++++++
>>   3 files changed, 218 insertions(+), 5 deletions(-)
>>
>> diff --git a/configure b/configure
>> index f57fcc6..b5bf7d4 100755
>> --- a/configure
>> +++ b/configure
>> @@ -1956,6 +1956,62 @@ EOF
>>   /*
>>    * If we have stable libs the we don't want the libxc compat
>>    * layers, regardless of what CFLAGS we may have been given.
>> + *
>> + * Also, check if xengnttab_grant_copy_segment_t is defined and
>> + * grant copy operation is implemented.
>> + */
>> +#undef XC_WANT_COMPAT_EVTCHN_API
>> +#undef XC_WANT_COMPAT_GNTTAB_API
>> +#undef XC_WANT_COMPAT_MAP_FOREIGN_API
>> +#include <xenctrl.h>
>> +#include <xenstore.h>
>> +#include <xenevtchn.h>
>> +#include <xengnttab.h>
>> +#include <xenforeignmemory.h>
>> +#include <stdint.h>
>> +#include <xen/hvm/hvm_info_table.h>
>> +#if !defined(HVM_MAX_VCPUS)
>> +# error HVM_MAX_VCPUS not defined
>> +#endif
>> +int main(void) {
>> +  xc_interface *xc = NULL;
>> +  xenforeignmemory_handle *xfmem;
>> +  xenevtchn_handle *xe;
>> +  xengnttab_handle *xg;
>> +  xen_domain_handle_t handle;
>> +  xengnttab_grant_copy_segment_t* seg = NULL;
>> +
>> +  xs_daemon_open();
>> +
>> +  xc = xc_interface_open(0, 0, 0);
>> +  xc_hvm_set_mem_type(0, 0, HVMMEM_ram_ro, 0, 0);
>> +  xc_domain_add_to_physmap(0, 0, XENMAPSPACE_gmfn, 0, 0);
>> +  xc_hvm_inject_msi(xc, 0, 0xf0000000, 0x00000000);
>> +  xc_hvm_create_ioreq_server(xc, 0, HVM_IOREQSRV_BUFIOREQ_ATOMIC, NULL);
>> +  xc_domain_create(xc, 0, handle, 0, NULL, NULL);
>> +
>> +  xfmem = xenforeignmemory_open(0, 0);
>> +  xenforeignmemory_map(xfmem, 0, 0, 0, 0, 0);
>> +
>> +  xe = xenevtchn_open(0, 0);
>> +  xenevtchn_fd(xe);
>> +
>> +  xg = xengnttab_open(0, 0);
>> +  xengnttab_map_grant_ref(xg, 0, 0, 0);
>
> I don't think you need to check xengnttab_map_grant_ref, just
> xengnttab_grant_copy should be enough? Since xengnttab_grant_copy was added
> later you can assume xengnttab_map_grant_ref will be there.
>
>> +  xengnttab_grant_copy(xg, 0, seg);
>> +
>> +  return 0;
>> +}
>> +EOF
>> +      compile_prog "" "$xen_libs $xen_stable_libs"
>> +    then
>> +    xen_ctrl_version=480
>> +    xen=yes
>> +  elif
>> +      cat > $TMPC <<EOF &&
>> +/*
>> + * If we have stable libs the we don't want the libxc compat
>> + * layers, regardless of what CFLAGS we may have been given.
>>    */
>>   #undef XC_WANT_COMPAT_EVTCHN_API
>>   #undef XC_WANT_COMPAT_GNTTAB_API
>> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
>> index 3b8ad33..2dd1464 100644
>> --- a/hw/block/xen_disk.c
>> +++ b/hw/block/xen_disk.c
>> @@ -119,6 +119,9 @@ struct XenBlkDev {
>>       unsigned int        persistent_gnt_count;
>>       unsigned int        max_grants;
>>
>> +    /* Grant copy */
>> +    gboolean            feature_grant_copy;
>> +
>>       /* qemu block driver */
>>       DriveInfo           *dinfo;
>>       BlockBackend        *blk;
>> @@ -489,6 +492,95 @@ static int ioreq_map(struct ioreq *ioreq)
>>       return 0;
>>   }
>>
>> +static void free_buffers(struct ioreq *ioreq)
>> +{
>> +    int i;
>> +
>> +    for (i = 0; i < ioreq->v.niov; i++) {
>> +        ioreq->page[i] = NULL;
>> +    }
>> +
>> +    qemu_vfree(ioreq->pages);
>> +}
>> +
>> +static int ioreq_init_copy_buffers(struct ioreq *ioreq)
>> +{
>> +    int i;
>> +
>> +    if (ioreq->v.niov == 0) {
>> +        return 0;
>> +    }
>> +
>> +    ioreq->pages = qemu_memalign(XC_PAGE_SIZE, ioreq->v.niov * XC_PAGE_SIZE);
>> +    if (!ioreq->pages) {
>> +        return -1;
>> +    }
>> +
>> +    for (i = 0; i < ioreq->v.niov; i++) {
>> +        ioreq->page[i] = ioreq->pages + i * XC_PAGE_SIZE;
>> +        ioreq->v.iov[i].iov_base = ioreq->page[i];
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +static int ioreq_copy(struct ioreq *ioreq)
>> +{
>> +    xengnttab_handle *gnt = ioreq->blkdev->xendev.gnttabdev;
>> +    xengnttab_grant_copy_segment_t segs[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>> +    int i, count = 0, r, rc;
>
> Why do you need to initialize count to 0 here? A couple of lines below you
> inconditionally set it to ioreq->v.niov.
>
>> +    int64_t file_blk = ioreq->blkdev->file_blk;
>> +
>> +    if (ioreq->v.niov == 0) {
>> +        return 0;
>> +    }
>> +
>> +    count = ioreq->v.niov;
>> +
>> +    for (i = 0; i < count; i++) {
>> +
>> +        if (ioreq->req.operation == BLKIF_OP_READ) {
>> +            segs[i].flags = GNTCOPY_dest_gref;
>> +            segs[i].dest.foreign.ref = ioreq->refs[i];
>> +            segs[i].dest.foreign.domid = ioreq->domids[i];
>> +            segs[i].dest.foreign.offset = ioreq->req.seg[i].first_sect * file_blk;
>> +            segs[i].source.virt = ioreq->v.iov[i].iov_base;
>> +        } else {
>> +            segs[i].flags = GNTCOPY_source_gref;
>> +            segs[i].source.foreign.ref = ioreq->refs[i];
>> +            segs[i].source.foreign.domid = ioreq->domids[i];
>> +            segs[i].source.foreign.offset = ioreq->req.seg[i].first_sect * file_blk;
>> +            segs[i].dest.virt = ioreq->v.iov[i].iov_base;
>> +        }
>> +        segs[i].len = (ioreq->req.seg[i].last_sect
>> +                       - ioreq->req.seg[i].first_sect + 1) * file_blk;
>> +
>> +    }
>> +
>> +    rc = xengnttab_grant_copy(gnt, count, segs);
>> +
>> +    if (rc) {
>> +        xen_be_printf(&ioreq->blkdev->xendev, 0,
>> +                      "failed to copy data %d\n", rc);
>> +        ioreq->aio_errors++;
>> +        return -1;
>> +    } else {
>> +        r = 0;
>> +    }
>
> Do you really need both r and rc here? I think you could just have rc and
> use it below also.
>
>> +    for (i = 0; i < count; i++) {
>> +        if (segs[i].status != GNTST_okay) {
>> +            xen_be_printf(&ioreq->blkdev->xendev, 3,
>> +                          "failed to copy data %d for gref %d, domid %d\n", rc,
>> +                          ioreq->refs[i], ioreq->domids[i]);
>> +            ioreq->aio_errors++;
>> +            r = -1;
>> +        }
>> +    }
>> +
>> +    return r;
>> +}
>> +
>>   static int ioreq_runio_qemu_aio(struct ioreq *ioreq);
>>
>>   static void qemu_aio_complete(void *opaque, int ret)
>
> Roger.
>

Paulina