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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v2 2/9] docs/specs, tools: define the PAGE_DATA flags field
The 32-bit field after count in a PAGE_DATA record is reserved, and
libxenguest and the Python stream validator reject a record which sets
it. The record's page_data is page_size bytes of uncompressed
contents per present page, and nothing in the record can say that it
is encoded otherwise, so pages cannot be sent compressed.
Turn that field into a flags field. Bits 7-0 identify the algorithm
used to encode page_data, 0x00 meaning none, and a restoring side must
fail on a value it does not implement. Bits 31-8 stay reserved, and a
restoring side must still reject a record which sets any of them,
overriding the general rule for reserved fields. Make libxenguest and
the Python validator enforce both rules, and check the length of
page_data according to the algorithm. Add test_page_data_flags for the
Python checks.
The specification's Future Extensions section requires a new record
type for any extension of an existing one. Also allow an existing type
to be extended in place when a receiver which predates the extension is
guaranteed to reject the extended record rather than misread it. For
PAGE_DATA, this holds for an encoding which leaves count and the pfn
array in plaintext and shortens page_data: an older libxenguest which
ignores the field fails its exact length check.
The stream version is not bumped. A zero flags field means what the
reserved field meant, and no other value is accepted.
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Marcus Granado <marcus.granado@xxxxxxxxxx>
---
Notes:
Changes in v2:
- Replaces v1 1/6, which added a PAGE_DATA_LZ4 record type: PAGE_DATA's
reserved field becomes a flags field, following review by Teddy
Astie and Frediano Ziglio. LZ4 is assigned in patch 3.
docs/specs/libxc-migration-stream.pandoc | 28 +++++++++++++++++------
tools/libs/guest/xg_sr_restore.c | 29 ++++++++++++++++--------
tools/libs/guest/xg_sr_stream_format.h | 8 ++++++-
tools/python/xen/migration/libxc.py | 28 ++++++++++++++++++-----
tools/python/xen/migration/tests.py | 25 +++++++++++++++++++-
5 files changed, 94 insertions(+), 24 deletions(-)
diff --git a/docs/specs/libxc-migration-stream.pandoc
b/docs/specs/libxc-migration-stream.pandoc
index b1c81b5d68..fd44dd6e0a 100644
--- a/docs/specs/libxc-migration-stream.pandoc
+++ b/docs/specs/libxc-migration-stream.pandoc
@@ -3,7 +3,8 @@
Andrew Cooper <<andrew.cooper3@xxxxxxxxxx>>
Wen Congyang <<wency@xxxxxxxxxxxxxx>>
Yang Hongyang <<hongyang.yang@xxxxxxxxxxxx>>
-% Revision 4
+ Marcus Granado <<marcus.granado@xxxxxxxxxx>>
+% Revision 5
Introduction
============
@@ -279,7 +280,7 @@ memory contents.
0 1 2 3 4 5 6 7 octet
+-----------------------+-------------------------+
- | count (C) | (reserved) |
+ | count (C) | flags |
+-----------------------+-------------------------+
| pfn[0] |
+-------------------------------------------------+
@@ -299,8 +300,19 @@ Field Description
----------- --------------------------------------------------------
count Number of pages described in this record.
-(reserved) Set to zero on save. A restoring side must reject a
- record with this field non-zero.
+flags Bit 7-0: Algorithm used to encode page_data.
+
+ 0x00: None. page_data is page_size octets of
+ uncompressed contents per present page.
+
+ 0x01 - 0xFF: Unassigned.
+
+ A restoring side must fail on an algorithm value it
+ does not implement, rather than attempting to
+ interpret the page_data.
+
+ Bit 31-8: Reserved. Set to zero on save. A restoring side
+ must reject a record with any of these bits set.
pfn An array of count PFNs and their types.
@@ -312,8 +324,8 @@ pfn An array of count PFNs and their types.
Bit 51-0: PFN.
-page_data page_size octets of uncompressed page contents for each
- page set as present in the pfn array.
+page_data Contents of each page set as present in the pfn array,
+ encoded with the algorithm in flags bits 7-0.
--------------------------------------------------------------------
Note: Count is strictly > 0. N is strictly <= C and it is possible for there
@@ -802,7 +814,9 @@ The format may be extended by adding additional record
types.
Extending an existing record type must be done by adding a new record
type. This allows old images with the old record to still be
-restored.
+restored. An existing record type may instead be extended in place if
+a receiver which predates the extension is guaranteed to reject the
+extended record rather than misread it.
The image header may only be extended by _appending_ additional
fields. In particular, the `marker`, `id` and `version` fields must
diff --git a/tools/libs/guest/xg_sr_restore.c b/tools/libs/guest/xg_sr_restore.c
index eae5a8e828..93b020b55f 100644
--- a/tools/libs/guest/xg_sr_restore.c
+++ b/tools/libs/guest/xg_sr_restore.c
@@ -401,10 +401,10 @@ static int handle_page_data(struct xc_sr_context *ctx,
struct xc_sr_record *rec)
}
/* Reject rather than ignore: a future use may change the layout. */
- if ( pages->_res1 != 0 )
+ if ( pages->flags & PAGE_DATA_FLAGS_RESZ_MASK )
{
- ERROR("Reserved field set in PAGE_DATA record: %#x",
- (unsigned int)pages->_res1);
+ ERROR("Reserved bits set in PAGE_DATA record: %#x",
+ (unsigned int)(pages->flags & PAGE_DATA_FLAGS_RESZ_MASK));
goto err;
}
@@ -463,13 +463,24 @@ static int handle_page_data(struct xc_sr_context *ctx,
struct xc_sr_record *rec)
types[i] = type;
}
- if ( rec->length != (sizeof(*pages) +
- (sizeof(uint64_t) * pages->count) +
- (PAGE_SIZE * pages_of_data)) )
+ switch ( pages->flags & PAGE_DATA_ALGO_MASK )
{
- ERROR("PAGE_DATA record wrong size: length %u, expected "
- "%zu + %zu + %lu", rec->length, sizeof(*pages),
- (sizeof(uint64_t) * pages->count), (PAGE_SIZE * pages_of_data));
+ case PAGE_DATA_ALGO_NONE:
+ if ( rec->length != (sizeof(*pages) +
+ (sizeof(uint64_t) * pages->count) +
+ (PAGE_SIZE * pages_of_data)) )
+ {
+ ERROR("PAGE_DATA record wrong size: length %u, expected "
+ "%zu + %zu + %lu", rec->length, sizeof(*pages),
+ (sizeof(uint64_t) * pages->count),
+ (PAGE_SIZE * pages_of_data));
+ goto err;
+ }
+ break;
+
+ default:
+ ERROR("Unsupported algorithm %u in PAGE_DATA record",
+ (unsigned int)(pages->flags & PAGE_DATA_ALGO_MASK));
goto err;
}
diff --git a/tools/libs/guest/xg_sr_stream_format.h
b/tools/libs/guest/xg_sr_stream_format.h
index 1e6e50a710..f839d874c8 100644
--- a/tools/libs/guest/xg_sr_stream_format.h
+++ b/tools/libs/guest/xg_sr_stream_format.h
@@ -83,10 +83,16 @@ struct xc_sr_rhdr
struct xc_sr_rec_page_data_header
{
uint32_t count;
- uint32_t _res1;
+ uint32_t flags;
uint64_t pfn[0];
};
+/* PAGE_DATA flags: bits 7-0 are the algorithm, bits 31-8 are reserved. */
+#define PAGE_DATA_ALGO_MASK 0x000000ffU
+#define PAGE_DATA_FLAGS_RESZ_MASK 0xffffff00U
+
+#define PAGE_DATA_ALGO_NONE 0x00000000U
+
#define PAGE_DATA_PFN_MASK 0x000fffffffffffffULL
#define PAGE_DATA_PFN_RESZ_MASK 0x0ff0000000000000ULL
#define PAGE_DATA_TYPE_MASK 0xf000000000000000ULL
diff --git a/tools/python/xen/migration/libxc.py
b/tools/python/xen/migration/libxc.py
index e52e632cb1..2906b78d36 100644
--- a/tools/python/xen/migration/libxc.py
+++ b/tools/python/xen/migration/libxc.py
@@ -86,6 +86,11 @@ PAGE_DATA_FORMAT = "II"
PAGE_DATA_PFN_MASK = (1 << 52) - 1
PAGE_DATA_PFN_RESZ_MASK = ((1 << 60) - 1) & ~((1 << 52) - 1)
+# page_data flags: bits 7-0 algorithm, bits 31-8 reserved (must reject)
+PAGE_DATA_ALGO_MASK = 0x000000ff
+PAGE_DATA_FLAGS_RESZ_MASK = 0xffffff00
+PAGE_DATA_ALGO_NONE = 0x00
+
# flags from xen/public/domctl.h: XEN_DOMCTL_PFINFO_* shifted by 32 bits
PAGE_DATA_TYPE_SHIFT = 60
PAGE_DATA_TYPE_LTABTYPE_MASK = (0x7 << PAGE_DATA_TYPE_SHIFT)
@@ -259,11 +264,14 @@ class VerifyLibxc(VerifyBase):
raise RecordError(
"PAGE_DATA record must be at least %d bytes long" % (minsz, ))
- count, res1 = unpack(PAGE_DATA_FORMAT, content[:minsz])
+ count, flags = unpack(PAGE_DATA_FORMAT, content[:minsz])
- if res1 != 0:
+ if flags & PAGE_DATA_FLAGS_RESZ_MASK:
raise StreamError(
- "Reserved bits set in PAGE_DATA record 0x%04x" % (res1, ))
+ "Reserved bits set in PAGE_DATA record 0x%08x"
+ % (flags & PAGE_DATA_FLAGS_RESZ_MASK, ))
+
+ algo = flags & PAGE_DATA_ALGO_MASK
pfnsz = count * 8
if (len(content) - minsz) < pfnsz:
@@ -289,9 +297,17 @@ class VerifyLibxc(VerifyBase):
nr_pages += 1
pagesz = nr_pages * 4096
- if len(content) != minsz + pfnsz + pagesz:
- raise RecordError("Expected %u + %u + %u, got %u" %
- (minsz, pfnsz, pagesz, len(content)))
+ datasz = len(content) - minsz - pfnsz
+
+ if algo == PAGE_DATA_ALGO_NONE:
+
+ if datasz != pagesz:
+ raise RecordError("Expected %u + %u + %u, got %u" %
+ (minsz, pfnsz, pagesz, len(content)))
+
+ else:
+ raise StreamError(
+ "Unsupported algorithm %u in PAGE_DATA record" % (algo, ))
def verify_record_x86_pv_info(self, content):
diff --git a/tools/python/xen/migration/tests.py
b/tools/python/xen/migration/tests.py
index fcf94b0bb2..1944ae09b3 100644
--- a/tools/python/xen/migration/tests.py
+++ b/tools/python/xen/migration/tests.py
@@ -6,7 +6,7 @@ Unit tests for migration v2 streams
import unittest
-from struct import calcsize
+from struct import calcsize, pack
from xen.migration import libxc, libxl
@@ -30,6 +30,29 @@ class TestLibxc(unittest.TestCase):
):
self.assertEqual(calcsize(fmt), sz)
+ def test_page_data_flags(self):
+ """ PAGE_DATA flags: algorithm dispatch and the reserved bits """
+
+ v = libxc.VerifyLibxc(lambda *_: None, lambda *_: b"")
+ PAGE = b"\x00" * 4096
+ NOTAB = libxc.PAGE_DATA_TYPE_NOTAB | 0x1 # one normal page, pfn 1
+
+ def rec(flags, data):
+ return pack(libxc.PAGE_DATA_FORMAT, 1, flags) + \
+ pack("=Q", NOTAB) + data
+
+ # Uncompressed: exactly one page of data, and nothing else accepted.
+ v.verify_record_page_data(rec(libxc.PAGE_DATA_ALGO_NONE, PAGE))
+ self.assertRaises(libxc.RecordError, v.verify_record_page_data,
+ rec(libxc.PAGE_DATA_ALGO_NONE, PAGE[:-1]))
+
+ # An unimplemented algorithm, and any reserved bit, are refused.
+ self.assertRaises(libxc.StreamError, v.verify_record_page_data,
+ rec(libxc.PAGE_DATA_ALGO_NONE + 1, PAGE))
+ for bit in range(8, 32):
+ self.assertRaises(libxc.StreamError, v.verify_record_page_data,
+ rec(1 << bit, PAGE))
+
class TestLibxl(unittest.TestCase):
--
2.43.0
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