On 22.12.2011, at 12:56, Christian Borntraeger wrote:
> From: Christian Borntraeger <borntrae...@de.ibm.com>
>
> On some cpus the overhead for virtualization instructions is in the same
> range as a system call. Having to call multiple ioctls to get set registers
> will make userspace handled exits more expensive than necessary.
> Lets provide two sections in kvm_run to have a shared save area for
> guest registers.
> 1. the first section is read-only, to handle registers that have side-effects
> 2. the second section is read/write, e.g. for general purpose registers.
>
>
> Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
> ---
> Documentation/virtual/kvm/api.txt | 16 ++++++++++++++++
> arch/ia64/include/asm/kvm.h | 7 +++++++
> arch/powerpc/include/asm/kvm.h | 7 +++++++
> arch/s390/include/asm/kvm.h | 6 ++++++
> arch/x86/include/asm/kvm.h | 7 +++++++
> include/linux/kvm.h | 13 +++++++++++++
> 6 files changed, 56 insertions(+)
>
> Index: b/Documentation/virtual/kvm/api.txt
> ===================================================================
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1652,7 +1652,23 @@ developer registration required to acces
> /* Fix the size of the union. */
> char padding[256];
> };
> + /* Here are two fields that allow to access often used registers
> + * directly, to avoid the overhead of the ioctl system call */
> + union {
> + /* registers which can be only read */
> + struct sync_ro_regs sync_ro_regs;
> + char padding[1024];
> + };
> + union {
> + /* read/write guest registers */
> + struct sync_rw_regs sync_rw_regs;
> + char padding[1024];
> + };
Why have 2 different structs?
Unions shouldn't be anonymous. Please give the union a name :).
Alex
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