From: mhkelley58@gmail.com
To: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
kirill.shutemov@linux.intel.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: [PATCH v2 8/8] x86/mm: Add comments about errors in set_memory_decrypted()/encrypted()
Date: Tue, 21 Nov 2023 13:20:16 -0800 [thread overview]
Message-ID: <20231121212016.1154303-9-mhklinux@outlook.com> (raw)
In-Reply-To: <20231121212016.1154303-1-mhklinux@outlook.com>
From: Michael Kelley <mhklinux@outlook.com>
The functions set_memory_decrypted()/encrypted() may leave the input
memory range in an inconsistent state if an error occurs. Add comments
describing the situation and what callers must be aware of. Also add
comments in __set_memory_enc_dec() with more details on the issues and
why further investment in error handling is not likely to be useful.
No functional change.
Suggested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
---
arch/x86/mm/pat/set_memory.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 7365c86a7ff0..f519e5ca543b 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2133,6 +2133,24 @@ int set_memory_global(unsigned long addr, int numpages)
/*
* __set_memory_enc_dec() is used for the hypervisors that get
* informed about "encryption" status via page tables.
+ *
+ * If an error occurs in making the transition between encrypted and
+ * decrypted, the transitioned memory is left in an indeterminate state.
+ * The encryption status in the guest page tables may not match the
+ * hypervisor's view of the encryption status, making the memory unusable.
+ * If the memory consists of multiple pages, different pages may be in
+ * different indeterminate states.
+ *
+ * It is difficult to recover from errors such that we can ensure
+ * consistency between the page tables and hypervisor view of the encryption
+ * state. It may not be possible to back out of changes, particularly if the
+ * failure occurs in communicating with the hypervisor. Given this limitation,
+ * further work on the error handling is not likely to meaningfully improve
+ * the reliablity or usability of the system.
+ *
+ * Any errors are likely to soon render the VM inoperable, but we return
+ * an error rather than panic'ing so that the caller can decide how best
+ * to shutdown cleanly.
*/
static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
{
@@ -2203,6 +2221,14 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
return set_memory_p(&addr, numpages);
}
+/*
+ * If set_memory_encrypted()/decrypted() returns an error, the input memory
+ * range is left in an indeterminate state. The encryption status of pages
+ * may be inconsistent, so the memory is unusable. The caller should not try
+ * to do further operations on the memory, or return it to the free list.
+ * The memory must be leaked, and the caller should take steps to shutdown
+ * the system as cleanly as possible as something is seriously wrong.
+ */
int set_memory_encrypted(unsigned long addr, int numpages)
{
return __set_memory_enc_dec(addr, numpages, true);
--
2.25.1
next prev parent reply other threads:[~2023-11-21 21:21 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 ` mhkelley58 [this message]
2023-11-24 10:06 ` [PATCH v2 0/8] x86/coco: Mark CoCo VM pages not present when changing encrypted state kirill.shutemov
2023-11-28 19:12 ` Michael Kelley
2023-11-29 15:10 ` kirill.shutemov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20231121212016.1154303-9-mhklinux@outlook.com \
--to=mhkelley58@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=ardb@kernel.org \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=decui@microsoft.com \
--cc=haiyangz@microsoft.com \
--cc=hch@infradead.org \
--cc=hpa@zytor.com \
--cc=jroedel@suse.de \
--cc=kirill.shutemov@linux.intel.com \
--cc=kys@microsoft.com \
--cc=linux-coco@lists.linux.dev \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=lstoakes@gmail.com \
--cc=luto@kernel.org \
--cc=mhklinux@outlook.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rick.p.edgecombe@intel.com \
--cc=sathyanarayanan.kuppuswamy@linux.intel.com \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=thomas.lendacky@amd.com \
--cc=urezki@gmail.com \
--cc=wei.liu@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).