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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 Tue, Jul 26, 2016 at 3:12 AM, George Dunlap <george.dunlap@xxxxxxxxxx> wrote:
> 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
Well, that's exactly what I did in an earlier version of the patch but
it was requested that I change it to something like this by Andrew
(see https://lists.xen.org/archives/html/xen-devel/2015-10/msg00434.html).
Then over the various iterations it ended up like looking like this.
Tamas
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