From: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Sean Christopherson <seanjc@google.com>,
Shuah Khan <shuah@kernel.org>,
x86@kernel.org, linux-sgx@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
Jia Zhang <zhang.jia@linux.alibaba.com>
Subject: Re: [PATCH v3 3/5] x86/sgx: Optimize the free_cnt count in sgx_epc_section
Date: Tue, 16 Feb 2021 11:30:13 +0800 [thread overview]
Message-ID: <483f1ff9-9022-b7fc-5931-79c0c83f1289@linux.alibaba.com> (raw)
In-Reply-To: <YCZyVXIeeYqNK+sy@kernel.org>
On 2/12/21 8:19 PM, Jarkko Sakkinen wrote:
> On Thu, Feb 11, 2021 at 02:04:12PM +0800, Tianjia Zhang wrote:
>> Hi,
>>
>> Sorry for the late reply.
>>
>> On 1/28/21 1:40 AM, Jarkko Sakkinen wrote:
>>> I could bet some money that this does not bring any significant
>>> performance gain.
>>>
>>
>> Yes, this does not bring performance gains. This is not a change for
>> performance, mainly to make the value of free_cnt look more accurate.
>>
>>> On Sun, Jan 24, 2021 at 02:29:05PM +0800, Tianjia Zhang wrote:
>>>> `section->free_cnt` represents the free page in sgx_epc_section,
>>>> which is assigned once after initialization. In fact, just after the
>>>> initialization is completed, the pages are in the `init_laundry_list`
>>>> list and cannot be allocated. This needs to be recovered by EREMOVE
>>>> of function sgx_sanitize_section() before it can be used as a page
>>>> that can be allocated. The sgx_sanitize_section() will be called in
>>>> the kernel thread ksgxd.
>>>>
>>>> This patch moves the initialization of `section->free_cnt` from the
>>>> initialization function `sgx_setup_epc_section()` to the function
>>>> `sgx_sanitize_section()`, and then accumulates the count after the
>>>
>>> Use single quotes instead of hyphens.
>>>>> successful execution of EREMOVE. This seems to be more reasonable,
>>>> free_cnt will also truly reflect the allocatable free pages in EPC.
>>>>
>>>> Sined-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
>>>> Reviewed-by: Sean Christopherson <seanjc@google.com>
>>>> ---
>>>> arch/x86/kernel/cpu/sgx/main.c | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
>>>> index 4465912174fd..e455ec7b3449 100644
>>>> --- a/arch/x86/kernel/cpu/sgx/main.c
>>>> +++ b/arch/x86/kernel/cpu/sgx/main.c
>>>> @@ -48,6 +48,7 @@ static void sgx_sanitize_section(struct sgx_epc_section *section)
>>>> if (!ret) {
>>>> spin_lock(§ion->lock);
>>>> list_move(&page->list, §ion->page_list);
>>>> + section->free_cnt++;
>>>> spin_unlock(§ion->lock);
>>>
>>> Someone can try to allocate a page while sanitize process is in progress.
>>>
>>> I think it is better to keep critical sections in the form that when you
>>> leave from one, the global state is legit.
>>>
>>
>> Do you mean to move the critical section to protect the entire while loop?
>> Of course, this is also possible, sanitize is a process only needed for
>> initialization, and the possibility of conflict is very small.
>>
>> Best regards,
>> Tianjia
>
> The big picture of this change to me, to be frank is that it's completely
> useless.
>
> Please start with the picture.
>
> /Jarkko
>
I carefully considered your suggestion, and I will delete 2/5 and 3/5 in
the next version.
Best regards,
Tianjia
next prev parent reply other threads:[~2021-02-16 3:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-24 6:29 [PATCH v3 0/5] Some optimizations related to sgx Tianjia Zhang
2021-01-24 6:29 ` [PATCH v3 1/5] selftests/x86: Simplify the code to get vdso base address in sgx Tianjia Zhang
2021-01-24 6:29 ` [PATCH v3 2/5] x86/sgx: Optimize the locking range in sgx_sanitize_section() Tianjia Zhang
2021-01-30 13:24 ` Jarkko Sakkinen
2021-01-24 6:29 ` [PATCH v3 3/5] x86/sgx: Optimize the free_cnt count in sgx_epc_section Tianjia Zhang
2021-01-27 17:40 ` Jarkko Sakkinen
2021-02-11 6:04 ` Tianjia Zhang
2021-02-12 12:19 ` Jarkko Sakkinen
2021-02-16 3:30 ` Tianjia Zhang [this message]
2021-01-24 6:29 ` [PATCH v3 4/5] x86/sgx: Allows ioctl PROVISION to execute before CREATE Tianjia Zhang
2021-01-30 13:26 ` Jarkko Sakkinen
2021-02-01 12:55 ` Tianjia Zhang
2021-01-24 6:29 ` [PATCH v3 5/5] x86/sgx: Remove redundant if conditions in sgx_encl_create Tianjia Zhang
2021-01-24 8:20 ` Greg KH
2021-01-25 18:46 ` Sean Christopherson
2021-01-30 14:33 ` Jarkko Sakkinen
2021-02-01 12:37 ` Tianjia Zhang
2021-01-25 17:22 ` [PATCH v3 0/5] Some optimizations related to sgx Jarkko Sakkinen
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