On 14.10.24 20:43, Heiko Carstens wrote:
On Mon, Oct 14, 2024 at 04:46:16PM +0200, David Hildenbrand wrote:
To support memory devices under QEMU/KVM, such as virtio-mem,
we have to prepare our kernel virtual address space accordingly and
have to know the highest possible physical memory address we might see
later: the storage limit. The good old SCLP interface is not suitable for
this use case.
In particular, memory owned by memory devices has no relationship to
storage increments, it is always detected using the device driver, and
unaware OSes (no driver) must never try making use of that memory.
Consequently this memory is located outside of the "maximum storage
increment"-indicated memory range.
Let's use our new diag500 STORAGE_LIMIT subcode to query this storage
limit that can exceed the "maximum storage increment", and use the
existing interfaces (i.e., SCLP) to obtain information about the initial
memory that is not owned+managed by memory devices.
If a hypervisor does not support such memory devices, the address exposed
through diag500 STORAGE_LIMIT will correspond to the maximum storage
increment exposed through SCLP.
To teach kdump on s390 to include memory owned by memory devices, there
will be ways to query the relevant memory ranges from the device via a
driver running in special kdump mode (like virtio-mem already implements
to filter /proc/vmcore access so we don't end up reading from unplugged
device blocks).
Tested-by: Mario Casquero <mcasquer@xxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
arch/s390/boot/physmem_info.c | 46 ++++++++++++++++++++++++++--
arch/s390/include/asm/physmem_info.h | 3 ++
2 files changed, 46 insertions(+), 3 deletions(-)
...
+static int diag500_storage_limit(unsigned long *max_physmem_end)
+{
+ register unsigned long __nr asm("1") = 0x4;
+ register unsigned long __storage_limit asm("2") = 0;
+ unsigned long reg1, reg2;
+ psw_t old;
In general we do not allow register asm usage anymore in s390 code,
except for a very few defined places. This is due to all the problems
that we've seen with code instrumentation and register corruption.
Makes sense. Note that I was inspired by GENERATE_KVM_HYPERCALL_FUNC
that also still uses register asm usage.
The patch below changes your code accordingly, but it is
untested. Please verify that your code still works.
Below LGTM, I'll give it a churn, thanks!
--
Cheers,
David / dhildenb
