linux-kernel - Re: [RFC PATCH] x86/sgx: Remove 'reclaim' boolean parameters

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Date: Mon, 19 Feb 2024 16:25:22 -0600
From: "Haitao Huang" <haitao.huang@...ux.intel.com>
To: "Dave Hansen" <dave.hansen@...el.com>, "Jarkko Sakkinen"
 <jarkko@...nel.org>
Cc: anakrish@...rosoft.com, bp@...en8.de, cgroups@...r.kernel.org,
 chrisyan@...rosoft.com, dave.hansen@...ux.intel.com, hpa@...or.com,
 kristen@...ux.intel.com, linux-kernel@...r.kernel.org,
 linux-sgx@...r.kernel.org, mikko.ylinen@...ux.intel.com, mingo@...hat.com,
 mkoutny@...e.com, seanjc@...gle.com, sohil.mehta@...el.com,
 tglx@...utronix.de, tim.c.chen@...ux.intel.com, tj@...nel.org, x86@...nel.org,
 yangjie@...rosoft.com, zhanb@...rosoft.com, zhiquan1.li@...el.com
Subject: Re: [RFC PATCH] x86/sgx: Remove 'reclaim' boolean parameters

On Mon, 19 Feb 2024 14:42:29 -0600, Jarkko Sakkinen <jarkko@...nel.org>  
wrote:

> On Mon Feb 19, 2024 at 3:56 PM UTC, Dave Hansen wrote:
>> On 2/19/24 07:39, Haitao Huang wrote:
>> > Remove all boolean parameters for 'reclaim' from the function
>> > sgx_alloc_epc_page() and its callers by making two versions of each
>> > function.
>> >
>> > Also opportunistically remove non-static declaration of
>> > __sgx_alloc_epc_page() and a typo
>> >
>> > Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
>> > Suggested-by: Jarkko Sakkinen <jarkko@...nel.org>
>> > ---
>> >  arch/x86/kernel/cpu/sgx/encl.c  | 56 +++++++++++++++++++++------
>> >  arch/x86/kernel/cpu/sgx/encl.h  |  6 ++-
>> >  arch/x86/kernel/cpu/sgx/ioctl.c | 23 ++++++++---
>> >  arch/x86/kernel/cpu/sgx/main.c  | 68  
>> ++++++++++++++++++++++-----------
>> >  arch/x86/kernel/cpu/sgx/sgx.h   |  4 +-
>> >  arch/x86/kernel/cpu/sgx/virt.c  |  2 +-
>> >  6 files changed, 115 insertions(+), 44 deletions(-)
>>
>> Jarkko, did this turn out how you expected?
>>
>> I think passing around a function pointer to *only* communicate 1 bit of
>> information is a _bit_ overkill here.
>>
>> Simply replacing the bool with:
>>
>> enum sgx_reclaim {
>> 	SGX_NO_RECLAIM,
>> 	SGX_DO_RECLAIM
>> };
>>
>> would do the same thing.  Right?
>>
>> Are you sure you want a function pointer for this?
>
> To look this in context I drafted quickly two branches representing
> imaginary next version of the patch set.
>
> I guess this would simpler and totally sufficient approach.
>
> With this approach I'd then change also:
>
> [PATCH v9 04/15] x86/sgx: Implement basic EPC misc cgroup functionality
>
> And add the enum-parameter already in that patch with just "no reclaim"
> enum. I.e. then 10/15 will add only "do reclaim" and the new
> functionality.
>
> BR, Jarkko
>

Thanks. My understanding is:

1) For this patch, replace the boolean with the enum as Dave suggested. No  
two versions of the same functions. And this is a prerequisite for the  
cgroup series, positioned before [PATCH v9 04/15]

2) For [PATCH v9 04/15], pass a hard coded SGX_NO_RECLAIM to  
sgx_epc_cg_try_charge() from sgx_alloc_epc_page().

3) For [PATCH v9 10/15], remove the hard coded value, pass the reclaim  
enum parameter value from sgx_alloc_epc_page() to  sgx_epc_cg_try_charge()  
and add the reclaim logic.

I'll send patches soon. But please let me know if I misunderstood.

Thanks
Haitao