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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v8] x86/mem-sharing: mem-sharing a range of memory
On Wed, Jul 20, 2016 at 7:01 PM, Tamas K Lengyel
<tamas.lengyel@xxxxxxxxxxxx> wrote:
> Currently mem-sharing can be performed on a page-by-page basis from the
> control
> domain. However, this process is quite wasteful when a range of pages have to
> be deduplicated.
>
> This patch introduces a new mem_sharing memop for range sharing where
> the user doesn't have to separately nominate each page in both the source and
> destination domain, and the looping over all pages happen in the hypervisor.
> This significantly reduces the overhead of sharing a range of memory.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>
> v8: style fixes and minor adjustments
> ---
> tools/libxc/include/xenctrl.h | 15 ++++
> tools/libxc/xc_memshr.c | 19 +++++
> tools/tests/mem-sharing/memshrtool.c | 22 ++++++
> xen/arch/x86/mm/mem_sharing.c | 140
> +++++++++++++++++++++++++++++++++++
> xen/include/public/memory.h | 10 ++-
> 5 files changed, 205 insertions(+), 1 deletion(-)
>
> diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
> index e904bd5..3782eff 100644
> --- a/tools/libxc/include/xenctrl.h
> +++ b/tools/libxc/include/xenctrl.h
> @@ -2334,6 +2334,21 @@ int xc_memshr_add_to_physmap(xc_interface *xch,
> domid_t client_domain,
> unsigned long client_gfn);
>
> +/* Allows to deduplicate a range of memory of a client domain. Using
> + * this function is equivalent of calling xc_memshr_nominate_gfn for each gfn
> + * in the two domains followed by xc_memshr_share_gfns.
> + *
> + * May fail with -EINVAL if the source and client domain have different
> + * memory size or if memory sharing is not enabled on either of the domains.
> + * May also fail with -ENOMEM if there isn't enough memory available to store
> + * the sharing metadata before deduplication can happen.
> + */
> +int xc_memshr_range_share(xc_interface *xch,
> + domid_t source_domain,
> + domid_t client_domain,
> + uint64_t start,
> + uint64_t end);
> +
> /* Debug calls: return the number of pages referencing the shared frame
> backing
> * the input argument. Should be one or greater.
> *
> diff --git a/tools/libxc/xc_memshr.c b/tools/libxc/xc_memshr.c
> index deb0aa4..2b871c7 100644
> --- a/tools/libxc/xc_memshr.c
> +++ b/tools/libxc/xc_memshr.c
> @@ -181,6 +181,25 @@ int xc_memshr_add_to_physmap(xc_interface *xch,
> return xc_memshr_memop(xch, source_domain, &mso);
> }
>
> +int xc_memshr_range_share(xc_interface *xch,
> + domid_t source_domain,
> + domid_t client_domain,
> + uint64_t start,
> + uint64_t end)
> +{
> + xen_mem_sharing_op_t mso;
> +
> + memset(&mso, 0, sizeof(mso));
> +
> + mso.op = XENMEM_sharing_op_range_share;
> +
> + mso.u.range.client_domain = client_domain;
> + mso.u.range.start = start;
> + mso.u.range.end = end;
> +
> + return xc_memshr_memop(xch, source_domain, &mso);
> +}
> +
> int xc_memshr_domain_resume(xc_interface *xch,
> domid_t domid)
> {
> diff --git a/tools/tests/mem-sharing/memshrtool.c
> b/tools/tests/mem-sharing/memshrtool.c
> index 437c7c9..2af6a9e 100644
> --- a/tools/tests/mem-sharing/memshrtool.c
> +++ b/tools/tests/mem-sharing/memshrtool.c
> @@ -24,6 +24,8 @@ static int usage(const char* prog)
> printf(" nominate <domid> <gfn> - Nominate a page for sharing.\n");
> printf(" share <domid> <gfn> <handle> <source> <source-gfn>
> <source-handle>\n");
> printf(" - Share two pages.\n");
> + printf(" range <source-domid> <destination-domid> <start-gfn>
> <end-gfn>\n");
> + printf(" - Share pages between domains in
> range.\n");
> printf(" unshare <domid> <gfn> - Unshare a page by grabbing a
> writable map.\n");
> printf(" add-to-physmap <domid> <gfn> <source> <source-gfn>
> <source-handle>\n");
> printf(" - Populate a page in a domain with a
> shared page.\n");
> @@ -180,6 +182,26 @@ int main(int argc, const char** argv)
> }
> printf("Audit returned %d errors.\n", rc);
> }
> + else if( !strcasecmp(cmd, "range") )
> + {
> + domid_t sdomid, cdomid;
> + int rc;
> + uint64_t start, end;
> +
> + if ( argc != 6 )
> + return usage(argv[0]);
>
> + sdomid = strtol(argv[2], NULL, 0);
> + cdomid = strtol(argv[3], NULL, 0);
> + start = strtoul(argv[4], NULL, 0);
> + end = strtoul(argv[5], NULL, 0);
> +
> + rc = xc_memshr_range_share(xch, sdomid, cdomid, start, end);
> + if ( rc < 0 )
> + {
> + printf("error executing xc_memshr_range_share: %s\n",
> strerror(errno));
> + return rc;
> + }
> + }
> return 0;
> }
> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
> index a522423..329fbd9 100644
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -1294,6 +1294,58 @@ int relinquish_shared_pages(struct domain *d)
> return rc;
> }
>
> +static int range_share(struct domain *d, struct domain *cd,
> + struct mem_sharing_op_range *range)
> +{
> + int rc = 0;
> + shr_handle_t sh, ch;
> + unsigned long start = range->_scratchspace ?: range->start;
> +
> + while( range->end >= start )
> + {
> + /*
> + * We only break out if we run out of memory as individual pages may
> + * legitimately be unsharable and we just want to skip over those.
> + */
> + rc = mem_sharing_nominate_page(d, start, 0, &sh);
> + if ( rc == -ENOMEM )
> + break;
> +
> + if ( !rc )
> + {
> + rc = mem_sharing_nominate_page(cd, start, 0, &ch);
> + if ( rc == -ENOMEM )
> + break;
> +
> + if ( !rc )
> + {
> + /* If we get here this should be guaranteed to succeed. */
> + rc = mem_sharing_share_pages(d, start, sh,
> + cd, start, ch);
> + ASSERT(!rc);
> + }
> + }
> +
> + /* Check for continuation if it's not the last iteration. */
> + if ( range->end >= ++start && hypercall_preempt_check() )
> + {
> + rc = 1;
> + break;
> + }
> + }
> +
> + range->_scratchspace = start;
> +
> + /*
> + * The last page may fail with -EINVAL, and for range sharing we don't
> + * care about that.
> + */
> + if ( range->end < start && rc == -EINVAL )
> + rc = 0;
> +
> + return rc;
> +}
> +
> int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
> {
> int rc;
> @@ -1468,6 +1520,94 @@ int
> mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
> }
> break;
>
> + case XENMEM_sharing_op_range_share:
> + {
> + unsigned long max_sgfn, max_cgfn;
> + struct domain *cd;
> +
> + rc = -EINVAL;
> + if ( mso.u.range._pad[0] || mso.u.range._pad[1] ||
> + mso.u.range._pad[2] )
> + goto out;
> +
> + /*
> + * We use _scratchscape for the hypercall continuation value.
> + * Ideally the user sets this to 0 in the beginning but
> + * there is no good way of enforcing that here, so we just check
> + * that it's at least in range.
> + */
> + if ( mso.u.range._scratchspace &&
> + (mso.u.range._scratchspace < mso.u.range.start ||
> + mso.u.range._scratchspace > mso.u.range.end) )
> + goto out;
> +
> + if ( !mem_sharing_enabled(d) )
> + goto out;
> +
> + rc = rcu_lock_live_remote_domain_by_id(mso.u.range.client_domain,
> + &cd);
> + if ( rc )
> + goto out;
> +
> + /*
> + * We reuse XENMEM_sharing_op_share XSM check here as this is
> + * essentially the same concept repeated over multiple pages.
> + */
> + rc = xsm_mem_sharing_op(XSM_DM_PRIV, d, cd,
> + XENMEM_sharing_op_share);
> + if ( rc )
> + {
> + rcu_unlock_domain(cd);
> + goto out;
> + }
> +
> + if ( !mem_sharing_enabled(cd) )
> + {
> + rcu_unlock_domain(cd);
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + /*
> + * Sanity check only, the client should keep the domains paused
> for
> + * the duration of this op.
> + */
> + if ( !atomic_read(&d->pause_count) ||
> + !atomic_read(&cd->pause_count) )
> + {
> + rcu_unlock_domain(cd);
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + max_sgfn = domain_get_maximum_gpfn(d);
> + max_cgfn = domain_get_maximum_gpfn(cd);
> +
> + if ( max_sgfn < mso.u.range.start || max_sgfn < mso.u.range.end
> ||
> + max_cgfn < mso.u.range.start || max_cgfn < mso.u.range.end )
> + {
> + rcu_unlock_domain(cd);
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + rc = range_share(d, cd, &mso.u.range);
> + rcu_unlock_domain(cd);
> +
> + if ( rc > 0 )
> + {
> + if ( __copy_to_guest(arg, &mso, 1) )
> + rc = -EFAULT;
> + else
> + rc =
> hypercall_create_continuation(__HYPERVISOR_memory_op,
> + "lh",
> XENMEM_sharing_op,
> + arg);
> + }
> + else
> + mso.u.range._scratchspace = 0;
> + }
> + break;
> +
> case XENMEM_sharing_op_debug_gfn:
> {
> unsigned long gfn = mso.u.debug.u.gfn;
> diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
> index 29ec571..e0bc018 100644
> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -465,6 +465,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_mem_access_op_t);
> #define XENMEM_sharing_op_debug_gref 5
> #define XENMEM_sharing_op_add_physmap 6
> #define XENMEM_sharing_op_audit 7
> +#define XENMEM_sharing_op_range_share 8
>
> #define XENMEM_SHARING_OP_S_HANDLE_INVALID (-10)
> #define XENMEM_SHARING_OP_C_HANDLE_INVALID (-9)
> @@ -500,7 +501,14 @@ struct xen_mem_sharing_op {
> uint64_aligned_t client_gfn; /* IN: the client gfn */
> uint64_aligned_t client_handle; /* IN: handle to the client page
> */
> domid_t client_domain; /* IN: the client domain id */
> - } share;
> + } share;
> + struct mem_sharing_op_range { /* OP_RANGE_SHARE */
> + uint64_aligned_t start; /* IN: start gfn. */
> + uint64_aligned_t end; /* IN: end gfn (inclusive) */
> + uint64_aligned_t _scratchspace; /* Must be set to 0 */
Tamas,
Why include this "scratchspace" that's not used in the interface,
rather than just doing what the memory operations in
xen/common/memory.c do, and store it in EAX by shifting it over by
MEMOP_EXTENT_SHIFT? I looked through the history and I see that v1
did something very much like that, but it was changed to using the
scratch space without any explanation.
Having this in the public interface is ugly; and what's worse, it
exposes some of the internal mechanism to the guest.
-George
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