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Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region
From: |
David Hildenbrand |
Subject: |
Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region |
Date: |
Mon, 27 Jul 2020 11:52:30 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 |
On 27.07.20 11:48, Cornelia Huck wrote:
> On Fri, 24 Jul 2020 16:37:47 +0200
> David Hildenbrand <david@redhat.com> wrote:
>
>> A guest OS that is aware of memory devices (placed into the device
>> memory region located in guest physical address space) has to know at least
>> the end address of the device memory region during boot, for example, to
>> prepare the kernel virtual address space accordingly (e.g., select page
>> table hierarchy). The device memory region is located above the SCLP
>> maximum storage increment.
>>
>> Let's provide a new diag500 subcode to query the location of the device
>> memory region under QEMU/KVM. This way, esp. Linux who's wants to support
>> virtio-based memory devices can query the location of this region and
>> derive the maximum possible PFN.
>>
>> Let's use a specification exception in case no such memory region
>> exists (e.g., maxmem wasn't specified, or on old QEMU machines). We'll
>> unlock this with future patches that prepare and instanciate the device
>> memory region.
>
> Specification exception on old machines seems reasonable. But maybe
> newer machines can use a different return value for "no memory regions"?
Hm, I don't see any benefit to distinguish the two cases of "no device
memory region". Should the guest really care?
[...]
>
> (...)
>
>> diff --git a/hw/s390x/s390-hypercall.h b/hw/s390x/s390-hypercall.h
>> index e6b958db41..1b179d7d99 100644
>> --- a/hw/s390x/s390-hypercall.h
>> +++ b/hw/s390x/s390-hypercall.h
>> @@ -16,6 +16,7 @@
>> #define DIAG500_VIRTIO_RESET 1 /* legacy */
>> #define DIAG500_VIRTIO_SET_STATUS 2 /* legacy */
>> #define DIAG500_VIRTIO_CCW_NOTIFY 3 /* KVM_S390_VIRTIO_CCW_NOTIFY */
>> +#define DIAG500_DEVICE_MEMORY_REGION 4
>
> Regardless what we end up with, this needs to be specified
> somewhere(tm).
>
Yeah, there, we should also document the existing subcodes. What would
be the right place for this? The kernel feels somewhat wrong to me.
--
Thanks,
David / dhildenb
- Re: [PATCH RFCv3 1/9] s390x: move setting of maximum ram size to machine init, (continued)
- [PATCH RFCv3 4/9] s390x: prepare for more diag500 hypercalls, David Hildenbrand, 2020/07/24
- [PATCH RFCv3 5/9] s390x: rename s390-virtio-hcall* to s390-hypercall*, David Hildenbrand, 2020/07/24
- [PATCH RFCv3 7/9] s390x: prepare device memory address space, David Hildenbrand, 2020/07/24
- [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, David Hildenbrand, 2020/07/24
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, Cornelia Huck, 2020/07/27
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region,
David Hildenbrand <=
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, Cornelia Huck, 2020/07/27
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, David Hildenbrand, 2020/07/27
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, Heiko Carstens, 2020/07/27
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, David Hildenbrand, 2020/07/27
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, Cornelia Huck, 2020/07/28
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, David Hildenbrand, 2020/07/29
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, Cornelia Huck, 2020/07/29
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, David Hildenbrand, 2020/07/29
- Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region, Cornelia Huck, 2020/07/29
[PATCH RFCv3 3/9] s390x: remove hypercall registration mechanism, David Hildenbrand, 2020/07/24