Re: [PATCH v4 13/18] x86/sgx: Expose sgx_reclaim_pages() for use by EPC cgroup

Jarkko Sakkinen
2023-09-13T15:36:12Z

On Wed Sep 13, 2023 at 7:06 AM EEST, Haitao Huang wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
>
> Adjust and expose the top-level reclaim function as
> sgx_reclaim_epc_pages() for use by the upcoming EPC cgroup, which will
> initiate reclaim to enforce the max limit.
>
> Make these adjustments to the function signature.
>
> 1) To take a parameter that specifies the number of pages to scan for
> reclaiming. Define a max value of 32, but scan 16 in the case for the
> global reclaimer (ksgxd). The EPC cgroup will use it to specify a
> desired number of pages to be reclaimed up to the max value of 32.
>
> 2) To take a flag to force reclaiming a page regardless of its age. The
> EPC cgroup will use the flag to enforce its limits by draining the
> reclaimable lists before resorting to other measures, e.g. forcefully
> kill enclaves.
>
> 3) Return the number of reclaimed pages. The EPC cgroup will use the
> result to track reclaiming progress and escalate to a more forceful
> reclaiming mode, e.g., calling this function with the flag to ignore age
> of pages.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
> Cc: Sean Christopherson <seanjc@google.com>
> ---
> V4:
> - Combined the 3 patches that made the individual changes to the
> function signature.
> - Removed 'high' limit in commit message.
> ---
> arch/x86/kernel/cpu/sgx/main.c | 30 ++++++++++++++++++++----------
> arch/x86/kernel/cpu/sgx/sgx.h | 1 +
> 2 files changed, 21 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index c8900d62cfff..e1dde431a400 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -17,6 +17,10 @@
> #include "driver.h"
> #include "encl.h"
> #include "encls.h"

newline here

> +/**

/*

> + * Maximum number of pages to scan for reclaiming.
> + */
> +#define SGX_NR_TO_SCAN_MAX 32
>
> struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
> static int sgx_nr_epc_sections;
> @@ -279,7 +283,11 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
> mutex_unlock(&encl->lock);
> }
>
> -/*
> +/**
> + * sgx_reclaim_epc_pages() - Reclaim EPC pages from the consumers
> + * @nr_to_scan: Number of EPC pages to scan for reclaim
> + * @ignore_age: Reclaim a page even if it is young
> + *
> * Take a fixed number of pages from the head of the active page pool and
> * reclaim them to the enclave's private shmem files. Skip the pages, which have
> * been accessed since the last scan. Move those pages to the tail of active
> @@ -292,15 +300,15 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
> * problematic as it would increase the lock contention too much, which would
> * halt forward progress.
> */
> -static void sgx_reclaim_pages(void)
> +size_t sgx_reclaim_epc_pages(size_t nr_to_scan, bool ignore_age)
> {
> - struct sgx_backing backing[SGX_NR_TO_SCAN];
> + struct sgx_backing backing[SGX_NR_TO_SCAN_MAX];
> struct sgx_epc_page *epc_page, *tmp;
> struct sgx_encl_page *encl_page;
> pgoff_t page_index;
> LIST_HEAD(iso);
> - int ret;
> - int i;
> + size_t ret;
> + size_t i;

I don't mind having these in separate lines but you could also

size_t ret, i;

>
> spin_lock(&sgx_global_lru.lock);
> for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> @@ -326,13 +334,14 @@ static void sgx_reclaim_pages(void)
> spin_unlock(&sgx_global_lru.lock);
>
> if (list_empty(&iso))
> - return;
> + return 0;
>
> i = 0;
> list_for_each_entry_safe(epc_page, tmp, &iso, list) {
> encl_page = epc_page->encl_page;
>
> - if (!sgx_reclaimer_age(epc_page))
> + if (i == SGX_NR_TO_SCAN_MAX ||
> + (!ignore_age && !sgx_reclaimer_age(epc_page)))
> goto skip;
>
> page_index = PFN_DOWN(encl_page->desc - encl_page->encl->base);
> @@ -371,6 +380,7 @@ static void sgx_reclaim_pages(void)
>
> sgx_free_epc_page(epc_page);
> }

newline

> + return i;
> }
>
> static bool sgx_should_reclaim(unsigned long watermark)
> @@ -387,7 +397,7 @@ static bool sgx_should_reclaim(unsigned long watermark)
> void sgx_reclaim_direct(void)
> {
> if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
> - sgx_reclaim_pages();
> + sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false);
> }
>
> static int ksgxd(void *p)
> @@ -410,7 +420,7 @@ static int ksgxd(void *p)
> sgx_should_reclaim(SGX_NR_HIGH_PAGES));
>
> if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
> - sgx_reclaim_pages();
> + sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false);
>
> cond_resched();
> }
> @@ -582,7 +592,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> break;
> }
>
> - sgx_reclaim_pages();
> + sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false);
> cond_resched();
> }
>
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 3818be5a8bd3..aa4ec2c0ce96 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -177,6 +177,7 @@ void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags);
> int sgx_drop_epc_page(struct sgx_epc_page *page);
> struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim);
> bool sgx_epc_oom(struct sgx_epc_lru_lists *lrus);
> +size_t sgx_reclaim_epc_pages(size_t nr_to_scan, bool ignore_age);
>
> void sgx_ipi_cb(void *info);
>
> --
> 2.25.1

BR, Jarkko