Re: [RFC PATCH 01/23] x86/sgx: Split out adding EPC page to free list to separate helper

Jarkko Sakkinen
2021-01-13T17:06:44Z

On Tue, Jan 12, 2021 at 01:45:24PM -0800, Sean Christopherson wrote:
> On Tue, Jan 12, 2021, Kai Huang wrote:
> > On Tue, 12 Jan 2021 00:38:40 +0200 Jarkko Sakkinen wrote:
> > > On Wed, 2021-01-06 at 14:55 +1300, Kai Huang wrote:
> > > > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > > >
> > > > SGX virtualization requires to allocate "raw" EPC and use it as virtual
> > > > EPC for SGX guest.  Unlike EPC used by SGX driver, virtual EPC doesn't
> > > > track how EPC pages are used in VM, e.g. (de)construction of enclaves,
> > > > so it cannot guarantee EREMOVE success, e.g. it doesn't have a priori
> > > > knowledge of which pages are SECS with non-zero child counts.
> > > >
> > > > Split sgx_free_page() into two parts so that the "add to free list"
> > > > part can be used by virtual EPC without having to modify the EREMOVE
> > > > logic in sgx_free_page().
> > > >
> > > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > > > Signed-off-by: Kai Huang <kai.huang@intel.com>
> > >
> > > I have a better idea with the same outcome for KVM.
> > >
> > > https://lore.kernel.org/linux-sgx/20210111223610.62261-1-jarkko@kernel.org/T/#t
> >
> > I agree with your patch this one can be replaced. I'll include your patch in
> > next version, and once it is upstreamed, it can be removed in my series.
> >
> > Sean, please let me know if you have objection.
>
> 6 of one, half dozen of the other. I liked not having to modify the existing
> call sites, but it's your code.

Only the call sites contained sgx_encl_release() require a call to
sgx_reset_epc_page(). That's three in total.

> Though on that topic, this snippet is wrong:
>
> @@ -431,7 +443,8 @@ void sgx_encl_release(struct kref *ref)
> va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
> list);
> list_del(&va_page->list);
> - sgx_free_epc_page(va_page->epc_page);
> + sgx_reset_epc_page(entry->epc_page);
> + sgx_free_epc_page(entry->epc_page);

Thanks for the remark.

I checked why I did not see this when running test_sgx. I had not specified
local tree for BuildRoot (LINUX_OVERRIDE_SRCDIR) when building test image.

> s/entry/va_page in the new code.
>
> P.S. I apparently hadn't been subscribed linux-sgx and so didn't see those
> patches. I'm now subscribed and can chime-in as needed.

OK, great, I can also CC directly to the next version.

/Jarkko