Jui-min Lee has uploaded this change for review. (
https://gem5-review.googlesource.com/c/public/gem5/+/57369 )
Change subject: mem: Fix phy mem with shm and multiple abstr mem
......................................................................
mem: Fix phy mem with shm and multiple abstr mem
Previously, all abstract memory backed by the same physical memory will
use the exact same chunk of shared memory if sharedBackstore is set. It
means that all abstract memories, despite setting to a different range,
will still be map to the same chunk of memory.
As a result, setting the sharedBackstore not only allows our host system
to share gem5 memory, it also enforces multiple gem5 memories to share
the same content. Which will significantly affect the simulation result.
Furthermore, the actual size of the shared memory will be determined by
the last backingStore created. If the last one is unfortunately smaller
than any previous backingStore, this may invalid previous mapped region
and cause a SIGBUS upon access (on linux).
In this CL, we put all backingStores of those abstract memories side by
side instead of stacking them all together. So the behavior of abstract
memories will be kept consistent whether the sharedBackstore is set or
not, yet presist the ability to access those memories from host.
Change-Id: Ic4ec25c99fe72744afaa2dfbb48cd0d65230e9a8
---
M src/mem/physical.cc
M src/mem/physical.hh
2 files changed, 39 insertions(+), 5 deletions(-)
diff --git a/src/mem/physical.cc b/src/mem/physical.cc
index ae20fb6..a7e261f 100644
--- a/src/mem/physical.cc
+++ b/src/mem/physical.cc
@@ -79,7 +79,7 @@
bool mmap_using_noreserve,
const std::string& shared_backstore) :
_name(_name), size(0), mmapUsingNoReserve(mmap_using_noreserve),
- sharedBackstore(shared_backstore)
+ sharedBackstore(shared_backstore), sharedBackstoreSize(0)
{
if (mmap_using_noreserve)
warn("Not reserving swap space. May cause SIGSEGV on actual
usage\n");
@@ -201,17 +201,22 @@
int shm_fd;
int map_flags;
+ off_t map_offset;
if (sharedBackstore.empty()) {
shm_fd = -1;
map_flags = MAP_ANON | MAP_PRIVATE;
+ map_offset = 0;
} else {
- DPRINTF(AddrRanges, "Sharing backing store as %s\n",
- sharedBackstore.c_str());
+ // Newly create backstore will be located after previous one.
+ map_offset = sharedBackstoreSize;
+ sharedBackstoreSize += range.size();
+ DPRINTF(AddrRanges, "Sharing backing store as %s at offset %llu\n",
+ sharedBackstore.c_str(), (uint64_t)map_offset);
shm_fd = shm_open(sharedBackstore.c_str(), O_CREAT | O_RDWR, 0666);
if (shm_fd == -1)
panic("Shared memory failed");
- if (ftruncate(shm_fd, range.size()))
+ if (ftruncate(shm_fd, sharedBackstoreSize))
panic("Setting size of shared memory failed");
map_flags = MAP_SHARED;
}
@@ -224,7 +229,7 @@
uint8_t* pmem = (uint8_t*) mmap(NULL, range.size(),
PROT_READ | PROT_WRITE,
- map_flags, shm_fd, 0);
+ map_flags, shm_fd, map_offset);
if (pmem == (uint8_t*) MAP_FAILED) {
perror("mmap");
diff --git a/src/mem/physical.hh b/src/mem/physical.hh
index b7ec8eb..bb90664 100644
--- a/src/mem/physical.hh
+++ b/src/mem/physical.hh
@@ -140,6 +140,7 @@
const bool mmapUsingNoReserve;
const std::string sharedBackstore;
+ uint64_t sharedBackstoreSize;
// The physical memory used to provide the memory in the simulated
// system
--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: Ic4ec25c99fe72744afaa2dfbb48cd0d65230e9a8
Gerrit-Change-Number: 57369
Gerrit-PatchSet: 1
Gerrit-Owner: Jui-min Lee <f...@google.com>
Gerrit-MessageType: newchange
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