Re: [PATCH v4 2/5] x86/sgx: Reduce the locking range in sgx_sanitize_section()

[Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>]

On 2/3/21 6:00 AM, Jarkko Sakkinen wrote:
> On Mon, Feb 01, 2021 at 09:26:50PM +0800, Tianjia Zhang wrote:
> > The spin lock of sgx_epc_section only locks the page_list. The
> > EREMOVE operation and init_laundry_list is not necessary in the
> > protection range of the spin lock. This patch reduces the lock
> > range of the spin lock in the function sgx_sanitize_section()
> > and only protects the operation of the page_list.
> >
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
>
> I'm not confident that this change has any practical value.
>
> /Jarkko

As a process executed during initialization, this optimization effect 
may not be obvious. If possible, this critical area can be moved outside 
to protect the entire while loop.

Best regards,
Tianjia
> > ---
> >   arch/x86/kernel/cpu/sgx/main.c | 11 ++++-------
> >   1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> > index c519fc5f6948..4465912174fd 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -41,20 +41,17 @@ static void sgx_sanitize_section(struct sgx_epc_section *section)
> >   		if (kthread_should_stop())
> >   			return;
> >   
> > -		/* needed for access to ->page_list: */
> > -		spin_lock(&section->lock);
> > -
> >   		page = list_first_entry(&section->init_laundry_list,
> >   					struct sgx_epc_page, list);
> >   
> >   		ret = __eremove(sgx_get_epc_virt_addr(page));
> > -		if (!ret)
> > +		if (!ret) {
> > +			spin_lock(&section->lock);
> >   			list_move(&page->list, &section->page_list);
> > -		else
> > +			spin_unlock(&section->lock);
> > +		} else
> >   			list_move_tail(&page->list, &dirty);
> >   
> > -		spin_unlock(&section->lock);
> > -
> >   		cond_resched();
> >   	}
> >   
> > --
> > 2.19.1.3.ge56e4f7