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3a1258399b
Currently, when using a true R/O NVDIMM (ROM memory backend) with a label
area, the VM can easily crash QEMU by trying to write to the label area,
because the ROM memory is mmap'ed without PROT_WRITE.
[root@vm-0 ~]# ndctl disable-region region0
disabled 1 region
[root@vm-0 ~]# ndctl zero-labels nmem0
-> QEMU segfaults
Let's remember whether we have a ROM memory backend and properly
reject the write request:
[root@vm-0 ~]# ndctl disable-region region0
disabled 1 region
[root@vm-0 ~]# ndctl zero-labels nmem0
zeroed 0 nmem
In comparison, on a system with a R/W NVDIMM:
[root@vm-0 ~]# ndctl disable-region region0
disabled 1 region
[root@vm-0 ~]# ndctl zero-labels nmem0
zeroed 1 nmem
For ACPI, just return "unsupported", like if no label exists. For spapr,
return "H_P2", similar to when no label area exists.
Could we rely on the "unarmed" property? Maybe, but it looks cleaner to
only disallow what certainly cannot work.
After all "unarmed=on" primarily means: cannot accept persistent writes. In
theory, there might be setups where devices with "unarmed=on" set could
be used to host non-persistent data (temporary files, system RAM, ...); for
example, in Linux, admins can overwrite the "readonly" setting and still
write to the device -- which will work as long as we're not using ROM.
Allowing writing label data in such configurations can make sense.
Message-ID: <20230906120503.359863-2-david@redhat.com>
Fixes:
|
||
|---|---|---|
| .. | ||
| authz | ||
| block | ||
| chardev | ||
| crypto | ||
| disas | ||
| exec | ||
| fpu | ||
| gdbstub | ||
| hw | ||
| io | ||
| libdecnumber | ||
| migration | ||
| monitor | ||
| net | ||
| qapi | ||
| qemu | ||
| qom | ||
| scsi | ||
| semihosting | ||
| standard-headers | ||
| sysemu | ||
| tcg | ||
| ui | ||
| user | ||
| elf.h | ||
| glib-compat.h | ||
| qemu-io.h | ||
| qemu-main.h | ||