RE: [PATCH v5 3/9] x86/sgx: Keep record for SGX VA and Guest page type

Zhang, Cathy
2022-05-23T00:06:46Z

Hi Jarkko,

> -----Original Message-----
> From: Jarkko Sakkinen <jarkko@kernel.org>
> Sent: Saturday, May 21, 2022 3:11 AM
> To: Zhang, Cathy <cathy.zhang@intel.com>; Li, Zhiquan1
> <zhiquan1.li@intel.com>
> Cc: linux-sgx@vger.kernel.org; x86@kernel.org; Chatre, Reinette
> <reinette.chatre@intel.com>; Hansen, Dave <dave.hansen@intel.com>; Raj,
> Ashok <ashok.raj@intel.com>; chao.p.peng@linux.intel.com; Zhong, Yang
> <yang.zhong@intel.com>
> Subject: Re: [PATCH v5 3/9] x86/sgx: Keep record for SGX VA and Guest page
> type
>
> On Fri, May 20, 2022 at 06:38:58PM +0800, Cathy Zhang wrote:
> > Regular enclave EPC pages have sgx_encl_page as their owner, but SGX
> > VA page and KVM guest EPC page are maintained by different owner
> > structures.
> >
> > SGX CPUSVN update requires to know the EPC page owner's status and
> > then decide how to handle the page.
> >
> > Keep a record of page type for SGX VA and KVM guest page while the
> > other EPC pages already have their type tracked, so that CPUSVN update
> > can get EPC page's owner by type and handle it then.
> >
> > Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>
> >
> > ---
> > Changes since v3:
> > - Rename SGX_EPC_PAGE_GUEST as SGX_EPC_PAGE_KVM_GUEST.
> (Suggested by
> > Jarkko, Sakkinen)
> > ---
> > arch/x86/kernel/cpu/sgx/sgx.h | 4 ++++
> > arch/x86/kernel/cpu/sgx/encl.c | 2 ++ arch/x86/kernel/cpu/sgx/virt.c
> > | 2 ++
> > 3 files changed, 8 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/sgx/sgx.h
> > b/arch/x86/kernel/cpu/sgx/sgx.h index f8ed9deac18b..4ad0e5396eef
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/sgx.h
> > +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> > @@ -28,6 +28,10 @@
> >
> > /* Pages on free list */
> > #define SGX_EPC_PAGE_IS_FREE BIT(1)
> > +/* VA page */
> > +#define SGX_EPC_PAGE_VA BIT(2)
> > +/* Pages allocated for KVM guest */
> > +#define SGX_EPC_PAGE_KVM_GUEST BIT(3)
> >
> > struct sgx_epc_page {
> > unsigned int section;
> > diff --git a/arch/x86/kernel/cpu/sgx/encl.c
> > b/arch/x86/kernel/cpu/sgx/encl.c index 08f39fa03a39..383abd538ac9
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/encl.c
> > +++ b/arch/x86/kernel/cpu/sgx/encl.c
> > @@ -912,6 +912,8 @@ struct sgx_epc_page *sgx_alloc_va_page(struct
> sgx_va_page *va_page)
> > return ERR_PTR(-EFAULT);
> > }
> >
> > + epc_page->flags |= SGX_EPC_PAGE_VA;
> > +
> > return epc_page;
> > }
> >
> > diff --git a/arch/x86/kernel/cpu/sgx/virt.c
> > b/arch/x86/kernel/cpu/sgx/virt.c index e953816d7c8b..104487b72fb8
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/virt.c
> > +++ b/arch/x86/kernel/cpu/sgx/virt.c
> > @@ -50,6 +50,8 @@ static int __sgx_vepc_fault(struct sgx_vepc *vepc,
> > if (IS_ERR(epc_page))
> > return PTR_ERR(epc_page);
> >
> > + epc_page->flags |= SGX_EPC_PAGE_KVM_GUEST;
>
> This would need to be synced up with SGX_EPC_IS_VEPC:
>
> https://lore.kernel.org/linux-sgx/694234d7-6a0d-e85f-f2f9-
> e52b4a61e1ec@intel.com/T/#t
>
> Otherwise, we have a chaos.
>
> Can you sync up with Zhiquan Li and find some common approach. IMHO, it
> might even sense to merge these patch sets into one. Then it would be easier
> to review them as a whole.

Thanks for showing the above related patches, Jarkko! I just take a quick look at that series,
AFAIK, __sgx_vepc_fault() will only be called during VM boot up to allocate physical EPC pages.
Then, host does not know how VM works with those pages. VM SGX driver will handle any errors itself.
So with the approach in that series, what it actually tracks is the vaddr in QEMU address space
for all EPC pages allocated to the VM. Does host need to track such information? QEMU side
should provide it easily I think. @Li, Zhiquan1.

>
> BR, Jarkko