Hi,
在 12/21/21 6:40 PM, David Hildenbrand 写道:
On 21.12.21 11:14, Eric Ren wrote:
Hi David,
Hi Eric,
I feel confused on this piece of code:
```
void release_mem_region_adjustable(resource_size_t start,
resource_size_t size)
{
... snip
/*
* All memory regions added from memory-hotplug path have the
* flag IORESOURCE_SYSTEM_RAM. If the resource does not have
* this flag, we know that we are dealing with a resource coming
* from HMM/devm. HMM/devm use another mechanism to add/release
* a resource. This goes via devm_request_mem_region and
* devm_release_mem_region.
* HMM/devm take care to release their resources when they want,
* so if we are dealing with them, let us just back off here.
*/
if (!(res->flags & IORESOURCE_SYSRAM)) {
break;
}
```
The comment says IORESOURCE_SYSTEM_RAM while IORESOURCE_SYSRAM is
actually used.
Is this a mistake?
IORESOURCE_SYSTEM_RAM is really just (IORESOURCE_MEM|IORESOURCE_SYSRAM)
So it's sufficient to check for IORESOURCE_SYSRAM ("release_mem_region"
implies that it's a mem region)
Thanks. My doubt is cleared.
The reason why I come to read about this is that, I got -EEXIST error from
add_memory_driver_managed() when I want to virtio_mem regions sitting on
Reserved
memory region like this in /proc/iomem:
```
fffc0000-183fffffff : Reserved
100000000-183fffffff : System RAM (virtio_mem)
1820000000-183fffffff : System RAM (virtio_mem) // --> plugged MB
```
That looks broken.
Where did the __request_mem_region(IORESOURCE_SYSTEM_RAM |
IORESOURCE_EXCLUSIVE) go?
How does the memory end up being marked reserved?
If it's exposed via a firmware-provided memory map, that's a spec
violation ...
Please see below.
EEXIST error happens after plug -> unplug -> plug testing, because the
hot-added region remains after unplug. The hot-added region is under
Reserved region. The IORESOURCE_SYSRAM flag check will skips to handle
children of the Reserved region.
Thanks in advance!
Can you elaborate more on the setup / use case?
Yes, with my special setup, the result above is expected, because
"Reserved" resource does
not have IORESOURCE_SYSRAM flag.
I'm doing a hack experirement, that makes virtio_mem use physical memory
from reserved memory
by using memmap=xxx kernel parameter, instead of using device memory
backended my hypervisor.
Thanks for your help, and sorry for the noise ;-）
Eric
