linux-kernel - Re: [PATCH v2 00/25] KVM SGX virtualization support

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Date:   Thu, 11 Mar 2021 09:44:07 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>, Borislav Petkov <bp@...en8.de>
Cc:     kvm@...r.kernel.org, x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org, seanjc@...gle.com, luto@...nel.org,
        dave.hansen@...el.com, rick.p.edgecombe@...el.com,
        haitao.huang@...el.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, jethro@...tanix.com,
        b.thiel@...teo.de, jmattson@...gle.com, joro@...tes.org,
        vkuznets@...hat.com, wanpengli@...cent.com, corbet@....net
Subject: Re: [PATCH v2 00/25] KVM SGX virtualization support

On Wed, 2021-03-10 at 20:01 +0200, Jarkko Sakkinen wrote:
> On Tue, Mar 09, 2021 at 10:30:37AM +0100, Borislav Petkov wrote:
> > On Tue, Mar 09, 2021 at 02:38:49PM +1300, Kai Huang wrote:
> > > This series adds KVM SGX virtualization support. The first 14 patches starting
> > > with x86/sgx or x86/cpu.. are necessary changes to x86 and SGX core/driver to
> > > support KVM SGX virtualization, while the rest are patches to KVM subsystem.
> > 
> > Ok, I guess I'll queue 1-14 once Sean doesn't find anything
> > objectionable then give Paolo an immutable commit to base the KVM stuff
> > ontop.
> > 
> > Unless folks have better suggestions, ofc.
> 
> I'm otherwise cool with that, except patch #2.
> 
> It's based on this series:
> 
> https://lore.kernel.org/linux-sgx/20210113233541.17669-1-jarkko@kernel.org/
> 
> It's not reasonable to create driver specific wrapper for
> sgx_free_epc_page() because there is exactly *2* call sites of the function
> in the driver.  The driver contains 10 call sites (11 after my NUMA patches
> have been applied) of sgx_free_epc_page() in total.
> 
> Instead, it is better to add explicit EREMOVE to those call sites.
> 
> The wrapper only trashes the codebase. I'm not happy with it, given all the
> trouble to make it clean and sound.

However, your change has side effort: it always put page back into free pool, even
EREMOVE fails. To make your change w/o having any functional change, it has to be:

	if(!sgx_reset_epc_page())
		sgx_free_epc_page();

And for this, Dave raised one concern we should add a WARN() to let user know EPC
page is leaked, and reboot is requied to get them back.

However with sgx_reset_epc_page(), there's no place to add such WARN(), and
implementing original sgx_free_epc_page() as sgx_encl_free_epc_page() looks very
reasonable to me:

https://www.spinics.net/lists/linux-sgx/msg04631.html

Hi Dave,

What is your comment here?

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