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

From: Sean Christopherson <seanjc@google.com>
To: Kai Huang <kai.huang@intel.com>
Cc: Jarkko Sakkinen <jarkko@kernel.org>,
	linux-sgx@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org,
	luto@kernel.org, dave.hansen@intel.com, haitao.huang@intel.com,
	pbonzini@redhat.com, bp@alien8.de, tglx@linutronix.de,
	mingo@redhat.com, hpa@zytor.com
Subject: Re: [RFC PATCH 01/23] x86/sgx: Split out adding EPC page to free list to separate helper
Date: Tue, 12 Jan 2021 13:45:24 -0800	[thread overview]
Message-ID: <X/4YdCN9LwZGompH@google.com> (raw)
In-Reply-To: <20210112131944.9d69bb30cf4b94b6f6f25e7b@intel.com>

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.

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);

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.
