Re: [RFC PATCH 1/3] KVM: promote KVM_MEMSLOT_INCOHERENT to uapi

[Christoffer Dall <christoffer.dall@linaro.org>]

On Wed, Mar 18, 2015 at 03:10:31PM -0400, Andrew Jones wrote:
> Also rename to KVM_MEM_UNCACHED.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  Documentation/virtual/kvm/api.txt | 16 ++++++++++------
>  arch/arm/include/uapi/asm/kvm.h   |  1 +
>  arch/arm/kvm/arm.c                |  1 +
>  arch/arm/kvm/mmu.c                |  4 ++--
>  arch/arm64/include/uapi/asm/kvm.h |  1 +
>  include/linux/kvm_host.h          |  1 -
>  include/uapi/linux/kvm.h          |  2 ++
>  virt/kvm/kvm_main.c               |  7 ++++++-
>  8 files changed, 23 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 0007fef4ed814..a5a51403a7937 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -902,6 +902,7 @@ struct kvm_userspace_memory_region {
>  /* for kvm_memory_region::flags */
>  #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
>  #define KVM_MEM_READONLY	(1UL << 1)
> +#define KVM_MEM_UNCACHED	(1UL << 2)
>  
>  This ioctl allows the user to create or modify a guest physical memory
>  slot.  When changing an existing slot, it may be moved in the guest
> @@ -917,12 +918,15 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
>  be identical.  This allows large pages in the guest to be backed by large
>  pages in the host.
>  
> -The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and
> -KVM_MEM_READONLY.  The former can be set to instruct KVM to keep track of
> -writes to memory within the slot.  See KVM_GET_DIRTY_LOG ioctl to know how to
> -use it.  The latter can be set, if KVM_CAP_READONLY_MEM capability allows it,
> -to make a new slot read-only.  In this case, writes to this memory will be
> -posted to userspace as KVM_EXIT_MMIO exits.
> +The flags field supports three flags: KVM_MEM_LOG_DIRTY_PAGES,
> +KVM_MEM_READONLY, and KVM_MEM_UNCACHED.  The first can be set to instruct
> +KVM to keep track of writes to memory within the slot.  See KVM_GET_DIRTY_LOG
> +ioctl to know how to use it.  The second can be set, if KVM_CAP_READONLY_MEM
> +capability allows it, to make a new slot read-only.  In this case, writes to
> +this memory will be posted to userspace as KVM_EXIT_MMIO exits. The third can
> +be set, if the KVM_CAP_UNCACHED_MEM capability allows it. This remaps the
> +memory as uncached, i.e. userspace will always directly read/write RAM for
> +this memory region.

I would repeat the definition of the flag in the text here instead of
referring to the 'first', 'second', and 'third' here; it's too hard to
follow.

Also, which combination of these flags are allowed?  Can they all be set
in combination or are they mutually exclusive or a bit of everything?

Thanks,
-Christoffer