On Tue, Oct 22, 2019 at 03:49:22PM -0700, Sean Christopherson wrote:
> Move the reclaim logic out of sgx_free_page() and into a standalone
> helper to avoid taking sgx_active_page_list_lock when the page is known
> to be unreclaimable, which is the vast majority of flows that free EPC
> pages.
>
> Movig reclaim logic to a separate function also eliminates any
> possibility of silently leaking a page because it is unexpectedly
> reclaimable (and being actively reclaimed).
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
>
> I really don't like the sgx_unmark_...() name, but couldn't come up with
> anything better. Suggestions welcome...
>
> arch/x86/kernel/cpu/sgx/encl.c | 3 ++-
> arch/x86/kernel/cpu/sgx/main.c | 32 ++++++++-----------------------
> arch/x86/kernel/cpu/sgx/reclaim.c | 32 +++++++++++++++++++++++++++++++
> arch/x86/kernel/cpu/sgx/sgx.h | 3 ++-
> 4 files changed, 44 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 8045f1ddfd62..22186d89042a 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -474,9 +474,10 @@ void sgx_encl_destroy(struct sgx_encl *encl)
> * The page and its radix tree entry cannot be freed
> * if the page is being held by the reclaimer.
> */
> - if (sgx_free_page(entry->epc_page))
> + if (sgx_unmark_page_reclaimable(entry->epc_page))
> continue;
>
> + sgx_free_page(entry->epc_page);
> encl->secs_child_cnt--;
> entry->epc_page = NULL;
> }
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 8e7557d3ff03..cfd8480ef563 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -108,45 +108,29 @@ struct sgx_epc_page *sgx_alloc_page(void *owner, bool reclaim)
> * sgx_free_page() - Free an EPC page
> * @page: pointer a previously allocated EPC page
> *
> - * EREMOVE an EPC page and insert it back to the list of free pages. If the
> - * page is reclaimable, delete it from the active page list.
> - *
> - * Return:
> - * 0 on success,
> - * -EBUSY if a reclaim is in progress
> + * EREMOVE an EPC page and insert it back to the list of free pages. The page
> + * must not be reclaimable.
> */
> -int sgx_free_page(struct sgx_epc_page *page)
> +void sgx_free_page(struct sgx_epc_page *page)
> {
> struct sgx_epc_section *section = sgx_epc_section(page);
> int ret;
>
> /*
> - * Remove the page from the active list if necessary. If the page
> - * is actively being reclaimed, i.e. RECLAIMABLE is set but the
> - * page isn't on the active list, return -EBUSY as we can't free
> - * the page at this time since it is "owned" by the reclaimer.
> + * Don't take sgx_active_page_list_lock when asserting the page isn't
> + * reclaimable, missing a WARN in the very rare case is preferable to
> + * unnecessarily taking a global lock in the common case.
> */
> - spin_lock(&sgx_active_page_list_lock);
> - if (page->desc & SGX_EPC_PAGE_RECLAIMABLE) {
> - if (list_empty(&page->list)) {
> - spin_unlock(&sgx_active_page_list_lock);
> - return -EBUSY;
> - }
> - list_del(&page->list);
> - page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> - }
> - spin_unlock(&sgx_active_page_list_lock);
> + WARN_ON_ONCE(page->desc & SGX_EPC_PAGE_RECLAIMABLE);
>
> ret = __eremove(sgx_epc_addr(page));
> if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
> - return -EIO;
> + return;
>
> spin_lock(§ion->lock);
> list_add_tail(&page->list, §ion->page_list);
> atomic_inc(&sgx_nr_free_pages);
> spin_unlock(§ion->lock);
> -
> - return 0;
> }
>
> static void __init sgx_free_epc_section(struct sgx_epc_section *section)
> diff --git a/arch/x86/kernel/cpu/sgx/reclaim.c b/arch/x86/kernel/cpu/sgx/reclaim.c
> index 8067ce1915a4..e64c810883ec 100644
> --- a/arch/x86/kernel/cpu/sgx/reclaim.c
> +++ b/arch/x86/kernel/cpu/sgx/reclaim.c
> @@ -125,6 +125,38 @@ void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
> spin_unlock(&sgx_active_page_list_lock);
> }
>
> +/**
> + * sgx_unmark_page_reclaimable() - Remove a page from the reclaim list
> + * @page: EPC page
> + *
> + * Clear the reclaimable flag and remove the page from the active page list.
> + *
> + * Return:
> + * 0 on success,
> + * -EBUSY if the page is in the process of being reclaimed
> + */
> +int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
> +{
> + /*
> + * Remove the page from the active list if necessary. If the page
> + * is actively being reclaimed, i.e. RECLAIMABLE is set but the
> + * page isn't on the active list, return -EBUSY as we can't free
> + * the page at this time since it is "owned" by the reclaimer.
> + */
> + spin_lock(&sgx_active_page_list_lock);
> + if (page->desc & SGX_EPC_PAGE_RECLAIMABLE) {
> + if (list_empty(&page->list)) {
> + spin_unlock(&sgx_active_page_list_lock);
> + return -EBUSY;
> + }
> + list_del(&page->list);
> + page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> + }
> + spin_unlock(&sgx_active_page_list_lock);
Would a WARN_ONCE() make sense when SGX_EPC_PAGE_RECLAIMABLE is not set,
or do we have a legit flow where this can happen?
/Jarkko
