Re: [PATCH] kvm-s390: userspace access to guest storage keys

[Avi Kivity <avi@redhat.com>]

On 05/06/2011 01:25 PM, Carsten Otte wrote:
> From: Carsten Otte<cotte@de.ibm.com>
>
> This patch gives userspace access to the guest visible storage keys. Three
> operations are supported:
> KVM_S390_KEYOP_SSKE for setting storage keys, similar to the set storage key
> extended (SSKE) instruction.
> KVM_S390_KEYOP_ISKE for reading storage key content, similar to the insert
> storage key extended (ISKE) instruction.
> KVM_s390_KEYOP_RRBE for reading and resetting the page reference bit, similar
> to the reset reference bit extended (RRBE) instruction.
> Note that all functions take userspace addresses as input, which typically
> differ from guest addresses.
>
> This work was requested by Alex Graf for guest live migration: Different from
> x86 the guest's view of dirty and reference information is not stored in the
> page table entrys that are part of the guest address space but are stored in
> the storage key instead. Thus, the storage key needs to be read, transfered,
> and written back on the migration target side.
>

And not in main memory, either?

> Signed-off-by: Carsten Otte<cotte@de.ibm.com>
> ---
>   arch/s390/include/asm/kvm_host.h |    4 +
>   arch/s390/kvm/kvm-s390.c         |  149 ++++++++++++++++++++++++++++++++++++++-
>   include/linux/kvm.h              |    7 +

Documentation/kvm/api.txt ++++++++++++

>   3 files changed, 157 insertions(+), 3 deletions(-)
>
> Index: linux-2.6/arch/s390/include/asm/kvm_host.h
> ===================================================================
> --- linux-2.6.orig/arch/s390/include/asm/kvm_host.h
> +++ linux-2.6/arch/s390/include/asm/kvm_host.h
> @@ -47,6 +47,10 @@ struct sca_block {
>   #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
>   #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
>
> +#define KVM_S390_KEYOP_SSKE 0x01
> +#define KVM_S390_KEYOP_ISKE 0x02
> +#define KVM_S390_KEYOP_RRBE 0x03

kvm_host.h is not exported to userspace.  Use asm/kvm.h instead.

<snip black magic>

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.