From: Kai Huang <kai.huang@intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org
Cc: "H . Peter Anvin" <hpa@zytor.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Tony Luck <tony.luck@intel.com>, Andi Kleen <ak@linux.intel.com>,
Wander Lairson Costa <wander@redhat.com>,
Isaku Yamahata <isaku.yamahata@gmail.com>,
marcelo.cerri@canonical.com, tim.gardner@canonical.com,
khalid.elmously@canonical.com, philip.cox@canonical.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support
Date: Fri, 22 Jul 2022 11:32:48 +1200 [thread overview]
Message-ID: <23e5ea743cba1359ebf8932600266ff6a650a150.camel@intel.com> (raw)
In-Reply-To: <d3808510-9974-258e-0c7b-9a76e0868d48@intel.com>
On Thu, 2022-07-21 at 09:08 -0700, Dave Hansen wrote:
> On 6/8/22 19:52, Kuppuswamy Sathyanarayanan wrote:
> > For shared buffer allocation, alternatives like using the DMA API is
> > also considered. Although it simpler to use, it is not preferred because
> > dma_alloc_*() APIs require a valid bus device as argument, which would
> > need converting the attestation driver into a platform device driver.
> > This is unnecessary, and since the attestation driver does not do real
> > DMA, there is no need to use real DMA APIs.
>
> Let's actually try to walk through the requirements for the memory
> allocation here.
>
> 1. The guest kernel needs to allocate some guest physical memory
> for the attestation data buffer
> 2. The guest physical memory must be mapped by the guest so that
> it can be read/written.
> 3. The guest mapping must be a "TDX Shared" mapping. Since all
> guest physical memory is "TDX Private" by default, something
> must convert the memory from Private->Shared.
> 4. If there are alias mappings with "TDX Private" page table
> permissions, those mappings must never be used while the page is
> in its shared state.
> 4a. load_unaligned_zeropad() must be prevented from being used
> on the page immediately preceding a Private alias to a Shared
> page.
> 5. Actions that increasingly fracture the direct map must be avoided.
> Attestation may happen many times and repeated allocations that
> fracture the direct map have performance consequences.
> 6. A softer requirement: presuming that bounce buffers won't be used
> for TDX devices *forever*, it would be nice to use a mechanism that
> will continue to work on systems that don't have swiotlb on.
>
> I think we've talked about three different solutions:
>
> == vmalloc() ==
>
> So, let's say we used a relatively plain vmalloc(). That's great for
> #1->#3 as long as the vmalloc() mapping gets the "TDX Shared" bit set
> properly on its PTEs. But, it falls over for *either* #4 or #5. If it
> leaves the direct map alone, it's exposed to load_unaligned_zeropad().
> If it unmaps the memory from the direct map, it runs afoul of #5.
>
> == order-1 + vmap() ==
>
> Let's now consider a vmalloc() variant: allocate a bunch of order-1
> pages and vmap() page[1], leaving page[0] as a guard page against
> load_unaligned_zeropad() on the direct map. That works, but it's an
> annoying amount of code.
>
> == swiotlb pages ==
>
> Using the swiotlb bounce buffer pages is the other proposed option.
> They already have a working kernel mapping and have already been
> converted. They are mitigated against load_unaligned_zeropad(). They
> do cause direct map fracturing, but only once since they're allocated
> statically. They don't increasingly degrade things. It's a one-time
> cost. Their interaction with #6 is not great.
>
> Did I miss anything? Does that accurately capture where we are?
We can also reserve a dedicated CMA, but Kirill didn't like it.
--
Thanks,
-Kai
next prev parent reply other threads:[~2022-07-21 23:33 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-09 2:52 [PATCH v8 0/5] Add TDX Guest Attestation support Kuppuswamy Sathyanarayanan
2022-06-09 2:52 ` [PATCH v8 1/5] x86/tdx: Add TDX Guest attestation interface driver Kuppuswamy Sathyanarayanan
2022-06-24 16:51 ` Dave Hansen
2022-06-27 14:50 ` Sathyanarayanan Kuppuswamy
2022-06-27 17:24 ` Dave Hansen
2022-06-30 23:50 ` Sathyanarayanan Kuppuswamy
2022-07-05 12:07 ` Kai Huang
2022-07-05 18:45 ` Sathyanarayanan Kuppuswamy
2022-07-05 18:52 ` Dave Hansen
2022-07-05 21:21 ` Sathyanarayanan Kuppuswamy
2022-07-05 22:31 ` Kai Huang
2022-07-06 22:27 ` Sathyanarayanan Kuppuswamy
2022-07-06 22:59 ` Kai Huang
2022-07-18 22:52 ` Sathyanarayanan Kuppuswamy
2022-06-09 2:52 ` [PATCH v8 2/5] x86/tdx: Add TDX Guest event notify interrupt support Kuppuswamy Sathyanarayanan
2022-06-20 12:33 ` Kai Huang
2022-06-20 15:44 ` Sathyanarayanan Kuppuswamy
2022-06-23 9:46 ` Kai Huang
2022-06-23 10:24 ` Kai Huang
2022-06-24 22:23 ` Sathyanarayanan Kuppuswamy
2022-06-24 23:41 ` Nakajima, Jun
2022-06-25 3:35 ` Yao, Jiewen
2022-06-27 11:21 ` Kai Huang
2022-06-27 14:56 ` Sathyanarayanan Kuppuswamy
2022-07-14 0:46 ` Sathyanarayanan Kuppuswamy
2022-07-14 10:42 ` Kai Huang
2022-07-14 20:55 ` Sathyanarayanan Kuppuswamy
2022-07-14 23:58 ` Kai Huang
2022-06-09 2:52 ` [PATCH v8 3/5] x86/mm: Make tdx_enc_status_changed() vmalloc address compatible Kuppuswamy Sathyanarayanan
2022-06-09 2:52 ` [PATCH v8 4/5] x86/mm: Add noalias variants of set_memory_*crypted() functions Kuppuswamy Sathyanarayanan
2022-06-24 13:19 ` Dave Hansen
2022-06-27 15:12 ` Kirill A. Shutemov
2022-06-27 18:24 ` Dave Hansen
2022-06-28 1:15 ` Kai Huang
2022-07-05 15:29 ` Kirill A. Shutemov
2022-07-18 14:22 ` Sathyanarayanan Kuppuswamy
2022-07-19 16:13 ` Kirill A. Shutemov
2022-07-19 17:10 ` Sathyanarayanan Kuppuswamy
2022-07-19 21:55 ` Kirill A. Shutemov
2022-07-20 14:56 ` Sathyanarayanan Kuppuswamy
2022-07-20 16:17 ` Kirill A. Shutemov
2022-07-20 16:58 ` Sathyanarayanan Kuppuswamy
2022-06-09 2:52 ` [PATCH v8 5/5] x86/tdx: Add Quote generation support Kuppuswamy Sathyanarayanan
2022-06-14 12:30 ` Wander Lairson Costa
2022-06-14 12:58 ` Sathyanarayanan Kuppuswamy
2022-07-21 16:08 ` Dave Hansen
2022-07-21 16:42 ` Sathyanarayanan Kuppuswamy
2022-07-21 16:49 ` Dave Hansen
2022-07-21 16:54 ` Sathyanarayanan Kuppuswamy
2022-07-21 17:02 ` Dave Hansen
2022-07-21 17:16 ` Sathyanarayanan Kuppuswamy
2022-07-21 17:19 ` Dave Hansen
2022-07-21 18:31 ` Sathyanarayanan Kuppuswamy
2022-07-21 18:42 ` Isaku Yamahata
2022-07-21 18:52 ` Dave Hansen
2022-07-21 18:57 ` Sathyanarayanan Kuppuswamy
2022-07-21 19:23 ` Dave Hansen
2022-07-21 22:08 ` Sathyanarayanan Kuppuswamy
2022-07-21 23:16 ` Kai Huang
2022-07-21 23:32 ` Kai Huang [this message]
2022-07-22 0:27 ` Dave Hansen
2022-07-22 19:05 ` Isaku Yamahata
2022-07-22 19:13 ` Dave Hansen
2022-07-22 21:18 ` Sathyanarayanan Kuppuswamy
2022-07-22 21:24 ` Dave Hansen
2022-07-25 20:19 ` Nakajima, Jun
2022-07-25 20:23 ` Dave Hansen
2022-07-25 21:56 ` Nakajima, Jun
2022-07-25 22:06 ` Sathyanarayanan Kuppuswamy
2022-08-09 6:20 ` Guorui Yu
2022-11-21 2:04 ` Guorui Yu
2022-11-21 2:26 ` Dave Hansen
2023-01-07 0:58 ` Erdem Aktas
2022-07-25 11:05 ` Kai Huang
2022-06-24 18:24 ` [PATCH v8 0/5] Add TDX Guest Attestation support Dave Hansen
2022-06-27 14:51 ` Sathyanarayanan Kuppuswamy
2022-06-27 18:51 ` Dave Hansen
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