linux-kernel - Re: [PATCH v38 16/24] x86/sgx: Add a page reclaimer

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Message-ID: <20200922140314.GA164527@linux.intel.com>
Date:   Tue, 22 Sep 2020 17:03:23 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Jethro Beekman <jethro@...tanix.com>,
        Jordan Hand <jorhand@...ux.microsoft.com>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        Chunyang Hui <sanqian.hcy@...fin.com>,
        Seth Moore <sethmo@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v38 16/24] x86/sgx: Add a page reclaimer

On Tue, Sep 22, 2020 at 12:45:38PM +0200, Borislav Petkov wrote:
> > + * %SGX_ENCL_PAGE_VA_OFFSET_MASK:	Holds the offset in the Version Array
> > + *					(VA) page for a swapped page.
> >   * %SGX_ENCL_PAGE_ADDR_MASK:		Holds the virtual address of the page.
> >   *
> >   * The page address for SECS is zero and is used by the subsystem to recognize
> 
> ...

So what's wrong over here?

> > @@ -86,24 +123,34 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
> >  {
> >  	unsigned long encl_size = secs->size + PAGE_SIZE;
> >  	struct sgx_epc_page *secs_epc;
> > +	struct sgx_va_page *va_page;
> >  	struct sgx_pageinfo pginfo;
> >  	struct sgx_secinfo secinfo;
> >  	struct file *backing;
> >  	long ret;
> >  
> > +	va_page = sgx_encl_grow(encl);
> > +	if (IS_ERR(va_page))
> > +		return PTR_ERR(va_page);
> > +	else if (va_page)
> 
> Not "else" simply?
> 
> AFAICT, sgx_encl_grow() would either return an ERR_PTR or the actual
> page...
> 
> Also, should the growing happen *after* the SECS validation?

Yes, it would make sense. I'll move it.

> Let's add some comment blurb about "Write back/invalidate an EPC page"
> to at least start to explain what that "ewb" is.

OK, I'll try to write something understandable.

> > +	spin_lock(&sgx_active_page_list_lock);
> > +	for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> > +		if (list_empty(&sgx_active_page_list))
> 
> Isn't it enough to do this once, i.e., not in the loop? You're holding
> sgx_active_page_list_lock...

I think that would make sense. Distantly analogous to the EINIT
discussion. Too complex code for yet to be known problem workloads I'd
say.


> >  static void sgx_sanitize_section(struct sgx_epc_section *section)
> 
> ...

Is this about documenting this function?

> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

Thanks, this was valuable feedback.

/Jarkko