Re: [PATCH v7 1/3] x86/sgx: Rename the owner field of struct sgx_epc_page as encl_owner

["Huang, Kai" <kai.huang@intel.com>]

On Thu, 2022-09-01 at 08:35 +0800, Zhiquan Li wrote:
> In order to avoid unnecessary casting, rename the 'owner' field of
> struct sgx_epc_page as 'encl_owner', and update all of references.

This changelog itself doesn't explain _why_ renaming 'owner' to 'encl_owner' can
avoid the explicit casting.  In fact, the reason is that you will use a 'union'
to separate the use of 'owner' of the EPC page (between SGX driver and virtual
EPC).  The rename is just to make the name more clear, but cannot really avoid
casting.

So I think there should be more sentences to explain here, such as "in order to
send SIGBUS to userspace hypervisor to allow it to inject #MC to guest, use
virtual EPC page's owner to be the userspace virtual address of the EPC page",
and after those you can say something like "in order to avoid casting, use a
union to separate the use of owner for SGX driver EPC page and virtual EPC page.
And rename owner of SGX driver EPC page to 'encl_owner' to be more specific",
etc.

That being said, I guess you can just merge this patch with your second patch,
which actually introduces the 'union' and uses the owner for virtual EPC page.
And in changelog you explain everything above to justify the patch.

Does this make sense?

> 
> Signed-off-by: Zhiquan Li <zhiquan1.li@intel.com>
> 
> ---
> Changes since V6:
> - Revise the commit message suggested by Jarkko.
>   Link: https://lore.kernel.org/linux-sgx/20220826160503.1576966-1-zhiquan1.li@intel.com/T/#mb201506ed06932438c82d48915cd4ceae9745bc2
> ---
>  arch/x86/kernel/cpu/sgx/main.c | 20 ++++++++++----------
>  arch/x86/kernel/cpu/sgx/sgx.h  |  2 +-
>  2 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 515e2a5f25bb..1315c69a733e 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -102,7 +102,7 @@ static void __sgx_sanitize_pages(struct list_head *dirty_page_list)
>  
>  static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
>  {
> -	struct sgx_encl_page *page = epc_page->owner;
> +	struct sgx_encl_page *page = epc_page->encl_owner;
>  	struct sgx_encl *encl = page->encl;
>  	struct sgx_encl_mm *encl_mm;
>  	bool ret = true;
> @@ -134,7 +134,7 @@ static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
>  
>  static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
>  {
> -	struct sgx_encl_page *page = epc_page->owner;
> +	struct sgx_encl_page *page = epc_page->encl_owner;
>  	unsigned long addr = page->desc & PAGE_MASK;
>  	struct sgx_encl *encl = page->encl;
>  	int ret;
> @@ -191,7 +191,7 @@ void sgx_ipi_cb(void *info)
>  static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
>  			 struct sgx_backing *backing)
>  {
> -	struct sgx_encl_page *encl_page = epc_page->owner;
> +	struct sgx_encl_page *encl_page = epc_page->encl_owner;
>  	struct sgx_encl *encl = encl_page->encl;
>  	struct sgx_va_page *va_page;
>  	unsigned int va_offset;
> @@ -244,7 +244,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
>  static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
>  				struct sgx_backing *backing)
>  {
> -	struct sgx_encl_page *encl_page = epc_page->owner;
> +	struct sgx_encl_page *encl_page = epc_page->encl_owner;
>  	struct sgx_encl *encl = encl_page->encl;
>  	struct sgx_backing secs_backing;
>  	int ret;
> @@ -306,7 +306,7 @@ static void sgx_reclaim_pages(void)
>  		epc_page = list_first_entry(&sgx_active_page_list,
>  					    struct sgx_epc_page, list);
>  		list_del_init(&epc_page->list);
> -		encl_page = epc_page->owner;
> +		encl_page = epc_page->encl_owner;
>  
>  		if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
>  			chunk[cnt++] = epc_page;
> @@ -320,7 +320,7 @@ static void sgx_reclaim_pages(void)
>  
>  	for (i = 0; i < cnt; i++) {
>  		epc_page = chunk[i];
> -		encl_page = epc_page->owner;
> +		encl_page = epc_page->encl_owner;
>  
>  		if (!sgx_reclaimer_age(epc_page))
>  			goto skip;
> @@ -359,7 +359,7 @@ static void sgx_reclaim_pages(void)
>  		if (!epc_page)
>  			continue;
>  
> -		encl_page = epc_page->owner;
> +		encl_page = epc_page->encl_owner;
>  		sgx_reclaimer_write(epc_page, &backing[i]);
>  
>  		kref_put(&encl_page->encl->refcount, sgx_encl_release);
> @@ -560,7 +560,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
>  	for ( ; ; ) {
>  		page = __sgx_alloc_epc_page();
>  		if (!IS_ERR(page)) {
> -			page->owner = owner;
> +			page->encl_owner = owner;
>  			break;
>  		}
>  
> @@ -603,7 +603,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>  
>  	spin_lock(&node->lock);
>  
> -	page->owner = NULL;
> +	page->encl_owner = NULL;
>  	if (page->poison)
>  		list_add(&page->list, &node->sgx_poison_page_list);
>  	else
> @@ -638,7 +638,7 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
>  	for (i = 0; i < nr_pages; i++) {
>  		section->pages[i].section = index;
>  		section->pages[i].flags = 0;
> -		section->pages[i].owner = NULL;
> +		section->pages[i].encl_owner = NULL;
>  		section->pages[i].poison = 0;
>  		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
>  	}
> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> index 0f2020653fba..4d88abccd12e 100644
> --- a/arch/x86/kernel/cpu/sgx/sgx.h
> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> @@ -33,7 +33,7 @@ struct sgx_epc_page {
>  	unsigned int section;
>  	u16 flags;
>  	u16 poison;
> -	struct sgx_encl_page *owner;
> +	struct sgx_encl_page *encl_owner;
>  	struct list_head list;
>  };
>