linux-kernel - Re: [PATCH 06/26] x86/sgx: Introduce RECLAIM_IN

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Message-ID: <Y3Qj8sIzwU925DOw@kernel.org>
Date:   Wed, 16 Nov 2022 01:42:42 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     dave.hansen@...ux.kernel.org, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        zhiquan1.li@...el.com, Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH 06/26] x86/sgx: Introduce RECLAIM_IN_PROGRESS flag for
 EPC pages

On Fri, Nov 11, 2022 at 10:35:11AM -0800, Kristen Carlson Accardi wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> Keep track of whether the EPC page is in the middle of being reclaimed
> and do not delete the page off the it's LRU if it has not yet finished

"off the it's LRU" ?

> being reclaimed.

I'm not sure how the description makes the change understandable.

> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 14 +++++++++-----
>  arch/x86/kernel/cpu/sgx/sgx.h  |  4 ++++
>  2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 3b09433ffd85..8c451071fa91 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -305,13 +305,15 @@ static void __sgx_reclaim_pages(void)
>  
>  		encl_page = epc_page->encl_owner;
>  
> -		if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
> +		if (kref_get_unless_zero(&encl_page->encl->refcount) != 0) {
> +			epc_page->flags |= SGX_EPC_PAGE_RECLAIM_IN_PROGRESS;
>  			chunk[cnt++] = epc_page;
> -		else
> +		} else {
>  			/* The owner is freeing the page. No need to add the
>  			 * page back to the list of reclaimable pages.
>  			 */
>  			epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> +		}
>  	}
>  	spin_unlock(&sgx_global_lru.lock);
>  
> @@ -337,6 +339,7 @@ static void __sgx_reclaim_pages(void)
>  
>  skip:
>  		spin_lock(&sgx_global_lru.lock);
> +		epc_page->flags &= ~SGX_EPC_PAGE_RECLAIM_IN_PROGRESS;
>  		sgx_epc_push_reclaimable(&sgx_global_lru, epc_page);
>  		spin_unlock(&sgx_global_lru.lock);
>  
> @@ -360,7 +363,8 @@ static void __sgx_reclaim_pages(void)
>  		sgx_reclaimer_write(epc_page, &backing[i]);
>  
>  		kref_put(&encl_page->encl->refcount, sgx_encl_release);
> -		epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> +		epc_page->flags &= ~(SGX_EPC_PAGE_RECLAIMER_TRACKED |
> +				     SGX_EPC_PAGE_RECLAIM_IN_PROGRESS);
>  
>  		sgx_free_epc_page(epc_page);
>  	}
> @@ -508,7 +512,7 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
>  void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags)
>  {
>  	spin_lock(&sgx_global_lru.lock);
> -	WARN_ON(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +	WARN_ON(page->flags & SGX_EPC_PAGE_RECLAIM_FLAGS);

Please, open code SGX_EPC_PAGE_RECLAIM_FLAGS. It only adds unnecassry
need to cross-reference to the header file.

Also, please describe the changes on how state flags are used before
and after this patch to the commit message.

>  	page->flags |= flags;
>  	if (flags & SGX_EPC_PAGE_RECLAIMER_TRACKED)
>  		sgx_epc_push_reclaimable(&sgx_global_lru, page);
> @@ -532,7 +536,7 @@ int sgx_drop_epc_page(struct sgx_epc_page *page)
>  	spin_lock(&sgx_global_lru.lock);
>  	if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
>  		/* The page is being reclaimed. */
> -		if (list_empty(&page->list)) {
> +		if (page->flags & SGX_EPC_PAGE_RECLAIM_IN_PROGRESS) {
>  			spin_unlock(&sgx_global_lru.lock);
>  			return -EBUSY;
>  		}
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 969606615211..04ca644928a8 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -30,6 +30,10 @@
>  #define SGX_EPC_PAGE_IS_FREE		BIT(1)
>  /* Pages allocated for KVM guest */
>  #define SGX_EPC_PAGE_KVM_GUEST		BIT(2)
> +/* page flag to indicate reclaim is in progress */
> +#define SGX_EPC_PAGE_RECLAIM_IN_PROGRESS BIT(3)
> +#define SGX_EPC_PAGE_RECLAIM_FLAGS	(SGX_EPC_PAGE_RECLAIMER_TRACKED | \
> +					 SGX_EPC_PAGE_RECLAIM_IN_PROGRESS)
>  
>  struct sgx_epc_page {
>  	unsigned int section;
> -- 
> 2.37.3
> 

BR, Jarkko