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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v6 2/2] xen: move TLB-flush filtering out into populate_physmap during vm creation
On 20/09/16 03:31, Dongli Zhang wrote:
> This patch implemented parts of TODO left in commit id
> a902c12ee45fc9389eb8fe54eeddaf267a555c58 (More efficient TLB-flush
> filtering in alloc_heap_pages()). It moved TLB-flush filtering out into
> populate_physmap. Because of TLB-flush in alloc_heap_pages, it's very slow
> to create a guest with memory size of more than 100GB on host with 100+
> cpus.
>
> This patch introduced a "MEMF_no_tlbflush" bit to memflags to indicate
> whether TLB-flush should be done in alloc_heap_pages or its caller
> populate_physmap. Once this bit is set in memflags, alloc_heap_pages will
> ignore TLB-flush. To use this bit after vm is created might lead to
> security issue, that is, this would make pages accessible to the guest B,
> when guest A may still have a cached mapping to them.
>
> Therefore, this patch also introduced a "creation_finished" field to struct
> domain to indicate whether this domain has ever got unpaused by hypervisor.
> MEMF_no_tlbflush can be set only during vm creation phase when
> creation_finished is still false before this domain gets unpaused for the
> first time.
>
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> ---
> Changed since v5:
> * Remove conditional check before "d->creation_finished = true;".
> * Place "bool creation_finished;" next to the other group of booleans.
> * Remove duplicate "only" in comments.
>
> Changed since v4:
> * Rename is_ever_unpaused to creation_finished.
> * Change bool_t to bool.
> * Polish comments.
>
> Changed since v3:
> * Set the flag to true in domain_unpause_by_systemcontroller when
> unpausing the guest domain for the first time.
> * Use true/false for all boot_t variables.
> * Add unlikely to optimize "if statement".
> * Correct comment style.
>
> Changed since v2:
> * Limit this optimization to domain creation time.
>
> ---
> xen/common/domain.c | 7 +++++++
> xen/common/memory.c | 22 ++++++++++++++++++++++
> xen/common/page_alloc.c | 4 +++-
> xen/include/xen/mm.h | 2 ++
> xen/include/xen/sched.h | 6 ++++++
> 5 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index a8804e4..3abaca9 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -1004,6 +1004,13 @@ int domain_unpause_by_systemcontroller(struct domain
> *d)
> {
> int old, new, prev = d->controller_pause_count;
>
> + /*
> + * We record this information here for populate_physmap to figure out
> + * that the domain has finished being created. In fact, we're only
> + * allowed to set the MEMF_no_tlbflush flag during VM creation.
> + */
> + d->creation_finished = true;
> +
> do
> {
> old = prev;
> diff --git a/xen/common/memory.c b/xen/common/memory.c
> index cc0f69e..21797ca 100644
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -141,6 +141,8 @@ static void populate_physmap(struct memop_args *a)
> unsigned int i, j;
> xen_pfn_t gpfn, mfn;
> struct domain *d = a->domain, *curr_d = current->domain;
> + bool need_tlbflush = false;
> + uint32_t tlbflush_timestamp = 0;
>
> if ( !guest_handle_subrange_okay(a->extent_list, a->nr_done,
> a->nr_extents-1) )
> @@ -150,6 +152,17 @@ static void populate_physmap(struct memop_args *a)
> max_order(curr_d)) )
> return;
>
> + /*
> + * With MEMF_no_tlbflush set, alloc_heap_pages() will ignore
> + * TLB-flushes. After VM creation, this is a security issue (it can
> + * make pages accessible to guest B, when guest A may still have a
> + * cached mapping to them). So we do this only during domain creation,
> + * when the domain itself has not yet been unpaused for the first
> + * time.
> + */
> + if ( unlikely(!d->creation_finished) )
> + a->memflags |= MEMF_no_tlbflush;
> +
> for ( i = a->nr_done; i < a->nr_extents; i++ )
> {
> if ( i != a->nr_done && hypercall_preempt_check() )
> @@ -214,6 +227,13 @@ static void populate_physmap(struct memop_args *a)
> goto out;
> }
>
> + if ( unlikely(a->memflags & MEMF_no_tlbflush) )
> + {
> + for ( j = 0; j < (1U << a->extent_order); j++ )
> + accumulate_tlbflush(&need_tlbflush, &page[j],
> + &tlbflush_timestamp);
> + }
> +
> mfn = page_to_mfn(page);
> }
>
> @@ -232,6 +252,8 @@ static void populate_physmap(struct memop_args *a)
> }
>
> out:
> + if ( need_tlbflush )
> + filtered_flush_tlb_mask(tlbflush_timestamp);
> a->nr_done = i;
> }
>
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index d7ca3a0..ae2476d 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -827,7 +827,9 @@ static struct page_info *alloc_heap_pages(
> BUG_ON(pg[i].count_info != PGC_state_free);
> pg[i].count_info = PGC_state_inuse;
>
> - accumulate_tlbflush(&need_tlbflush, &pg[i], &tlbflush_timestamp);
> + if ( !(memflags & MEMF_no_tlbflush) )
> + accumulate_tlbflush(&need_tlbflush, &pg[i],
> + &tlbflush_timestamp);
>
> /* Initialise fields which have other uses for free pages. */
> pg[i].u.inuse.type_info = 0;
> diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
> index 50db01d..76fbb82 100644
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -222,6 +222,8 @@ struct npfec {
> #define MEMF_exact_node (1U<<_MEMF_exact_node)
> #define _MEMF_no_owner 5
> #define MEMF_no_owner (1U<<_MEMF_no_owner)
> +#define _MEMF_no_tlbflush 6
> +#define MEMF_no_tlbflush (1U<<_MEMF_no_tlbflush)
> #define _MEMF_node 8
> #define MEMF_node_mask ((1U << (8 * sizeof(nodeid_t))) - 1)
> #define MEMF_node(n) ((((n) + 1) & MEMF_node_mask) << _MEMF_node)
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 2f9c15f..cd05e55 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -386,6 +386,12 @@ struct domain
> bool_t disable_migrate;
> /* Is this guest being debugged by dom0? */
> bool_t debugger_attached;
> + /*
> + * Set to true at the very end of domain creation, when the domain is
> + * unpaused for the first time by the systemcontroller.
> + */
> + bool creation_finished;
> +
> /* Which guest this guest has privileges on */
> struct domain *target;
>
>
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