From: Jarkko Sakkinen <jarkko@kernel.org>
To: Reinette Chatre <reinette.chatre@intel.com>
Cc: dave.hansen@linux.intel.com, md.iqbal.hossain@intel.com,
haitao.huang@intel.com, linux-sgx@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/sgx: Reduce delay and interference of enclave release
Date: Tue, 1 Nov 2022 02:52:16 +0200 [thread overview]
Message-ID: <Y2BtwGIfnW4fqkUg@kernel.org> (raw)
In-Reply-To: <77943714-b988-bf14-8795-c72ff0424418@intel.com>
On Mon, Oct 24, 2022 at 11:56:39AM -0700, Reinette Chatre wrote:
> Hi Jarkko,
>
> On 10/23/2022 1:06 PM, Jarkko Sakkinen wrote:
> > On Tue, Oct 18, 2022 at 03:42:47PM -0700, Reinette Chatre wrote:
>
> ...
>
> >> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> >> index 1ec20807de1e..f7365c278525 100644
> >> --- a/arch/x86/kernel/cpu/sgx/encl.c
> >> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> >> @@ -682,9 +682,12 @@ void sgx_encl_release(struct kref *ref)
> >> struct sgx_encl *encl = container_of(ref, struct sgx_encl, refcount);
> >> struct sgx_va_page *va_page;
> >> struct sgx_encl_page *entry;
> >> - unsigned long index;
> >> + unsigned long count = 0;
> >> +
> >> + XA_STATE(xas, &encl->page_array, PFN_DOWN(encl->base));
> >>
> >> - xa_for_each(&encl->page_array, index, entry) {
> >> + xas_lock(&xas);
> >> + xas_for_each(&xas, entry, PFN_DOWN(encl->base + encl->size - 1)) {
> >
> > I would add to declarations:
> >
> > unsigned long nr_pages = PFN_DOWN(encl->base + encl->size - 1);
> >
> > Makes this more readable.
>
> Will do, but I prefer to name it "max_page_index" or something related instead.
> "nr_pages" implies "number of pages" to me, which is not what
> PFN_DOWN(encl->base + encl->size - 1) represents. What is represented is the
> highest possible index of a page in page_array, where an index is the
> pfn of a page.
Yeah, makes sense.
>
> >
> >> if (entry->epc_page) {
> >> /*
> >> * The page and its radix tree entry cannot be freed
> >> @@ -699,9 +702,20 @@ void sgx_encl_release(struct kref *ref)
> >> }
> >>
> >> kfree(entry);
> >> - /* Invoke scheduler to prevent soft lockups. */
> >> - cond_resched();
> >> + /*
> >> + * Invoke scheduler on every XA_CHECK_SCHED iteration
> >> + * to prevent soft lockups.
> >> + */
> >> + if (!(++count % XA_CHECK_SCHED)) {
> >> + xas_pause(&xas);
> >> + xas_unlock(&xas);
> >> +
> >> + cond_resched();
> >> +
> >> + xas_lock(&xas);
> >> + }
> >> }
> >
> > WARN_ON(count != nr_pages);
> >
>
> nr_pages as assigned in your example does not represent a count of the
> enclave pages but instead a pfn index into the page_array. Comparing it
> to count, the number of removed enclave pages that are not being held
> by reclaimer, is not appropriate.
>
> This check would be problematic even if we create a "nr_pages" from
> the range of possible indices. This is because of how enclave sizes are
> required to be power-of-two that makes it likely for there to be indices
> without pages associated with it.
Ok.
>
> >> + xas_unlock(&xas);
> >>
> >> xa_destroy(&encl->page_array);
> >>
> >> --
> >> 2.34.1
> >>
>
> Reinette
BR, Jarkko
prev parent reply other threads:[~2022-11-01 0:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-18 22:42 [PATCH] x86/sgx: Reduce delay and interference of enclave release Reinette Chatre
2022-10-23 20:06 ` Jarkko Sakkinen
2022-10-24 18:56 ` Reinette Chatre
2022-11-01 0:52 ` Jarkko Sakkinen [this message]
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