From: kirill.shutemov@linux.intel.com
To: mhklinux@outlook.com
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org,
decui@microsoft.com, luto@kernel.org, peterz@infradead.org,
akpm@linux-foundation.org, urezki@gmail.com, hch@infradead.org,
lstoakes@gmail.com, thomas.lendacky@amd.com, ardb@kernel.org,
jroedel@suse.de, seanjc@google.com, rick.p.edgecombe@intel.com,
sathyanarayanan.kuppuswamy@linux.intel.com,
linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev,
linux-hyperv@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 0/8] x86/coco: Mark CoCo VM pages not present when changing encrypted state
Date: Fri, 24 Nov 2023 13:06:27 +0300 [thread overview]
Message-ID: <20231124100627.avltdnuhminwuzax@box> (raw)
In-Reply-To: <20231121212016.1154303-1-mhklinux@outlook.com>
On Tue, Nov 21, 2023 at 01:20:08PM -0800, mhkelley58@gmail.com wrote:
> From: Michael Kelley <mhklinux@outlook.com>
>
> In a CoCo VM when a page transitions from encrypted to decrypted, or vice
> versa, attributes in the PTE must be updated *and* the hypervisor must
> be notified of the change.
Strictly speaking it is not true for TDX. Conversion to shared can be
implicit: set shared bit and touch the page will do the conversion. MapGPA
is optional.
> Because there are two separate steps, there's
> a window where the settings are inconsistent. Normally the code that
> initiates the transition (via set_memory_decrypted() or
> set_memory_encrypted()) ensures that the memory is not being accessed
> during a transition, so the window of inconsistency is not a problem.
> However, the load_unaligned_zeropad() function can read arbitrary memory
> pages at arbitrary times, which could read a transitioning page during
> the window. In such a case, CoCo VM specific exceptions are taken
> (depending on the CoCo architecture in use). Current code in those
> exception handlers recovers and does "fixup" on the result returned by
> load_unaligned_zeropad(). Unfortunately, this exception handling can't
> work in paravisor scenarios (TDX Paritioning and SEV-SNP in vTOM mode)
> if the exceptions are routed to the paravisor. The paravisor can't
> do load_unaligned_zeropad() fixup, so the exceptions would need to
> be forwarded from the paravisor to the Linux guest, but there are
> no architectural specs for how to do that.
Hm. Can't we inject #PF (or #GP) into L2 if #VE/#VC handler in L1 sees
cross-page access to shared memory while no fixup entry for the page in
L1. It would give L2 chance to handle the situation in a transparent way.
Maybe I miss something, I donno.
--
Kiryl Shutsemau / Kirill A. Shutemov
next prev parent reply other threads:[~2023-11-24 10:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-21 21:20 [PATCH v2 0/8] x86/coco: Mark CoCo VM pages not present when changing encrypted state mhkelley58
2023-11-21 21:20 ` [PATCH v2 1/8] x86/coco: Use slow_virt_to_phys() in page transition hypervisor callbacks mhkelley58
2023-11-21 21:20 ` [PATCH v2 2/8] x86/mm: Don't do a TLB flush if changing a PTE that isn't marked present mhkelley58
2023-11-27 22:21 ` Edgecombe, Rick P
2023-11-28 17:34 ` Michael Kelley
2023-11-21 21:20 ` [PATCH v2 3/8] x86/mm: Remove "static" from vmap_pages_range() mhkelley58
2023-11-22 6:26 ` Christoph Hellwig
2023-11-23 0:24 ` Michael Kelley
2023-11-23 7:32 ` Christoph Hellwig
2023-11-27 1:06 ` Michael Kelley
2023-11-21 21:20 ` [PATCH v2 4/8] x86/sev: Enable PVALIDATE for PFNs without a valid virtual address mhkelley58
2023-11-27 21:38 ` Edgecombe, Rick P
2023-11-28 18:08 ` Michael Kelley
2023-11-28 18:59 ` Edgecombe, Rick P
2023-12-12 18:35 ` Michael Kelley
2023-11-21 21:20 ` [PATCH v2 5/8] x86/mm: Mark CoCo VM pages not present while changing encrypted state mhkelley58
2023-11-21 21:20 ` [PATCH v2 6/8] x86/mm: Merge CoCo prepare and finish hypervisor callbacks mhkelley58
2023-11-21 21:20 ` [PATCH v2 7/8] x86/mm: Remove unnecessary call layer for __set_memory_enc_pgtable() mhkelley58
2023-11-21 21:20 ` [PATCH v2 8/8] x86/mm: Add comments about errors in set_memory_decrypted()/encrypted() mhkelley58
2023-11-24 10:06 ` kirill.shutemov [this message]
2023-11-28 19:12 ` [PATCH v2 0/8] x86/coco: Mark CoCo VM pages not present when changing encrypted state Michael Kelley
2023-11-29 15:10 ` kirill.shutemov
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