On 01/09/2012 03:01 PM, Alexander Graf wrote:
> On 05.01.2012, at 10:54, Christian Borntraeger wrote:
>
> > 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 certain 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.
> > We also provide two 64bit flags fields (architecture specific), that will
> > specify which parts of these fields are valid. Each bit will define that
> > a group of registers (like general purpose) or a single register is valid.
> > In that way we can extend and shrink the interface. (The structure
> > definition
> > itself can only grow of course).
> >
> > Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
> > ---
> > Documentation/virtual/kvm/api.txt | 28 ++++++++++++++++++++++++++++
> > 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 | 20 ++++++++++++++++++++
> > 6 files changed, 75 insertions(+), 0 deletions(-)
> >
> > diff --git a/Documentation/virtual/kvm/api.txt
> > b/Documentation/virtual/kvm/api.txt
> > index da1f8fd..a149e22 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1693,6 +1693,34 @@ developer registration required to access it).
> > /* 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. Each
> > + * register can be extended or reduced by having flag bits
> > specifying
> > + * if a group of registers is valid.
> > + */
> > + __u64 kvm_valid_sync_ro_regs;
> > + __u64 kvm_valid_sync_rw_regs;
> > + union {
> > + /* registers which can be only read */
> > + struct kvm_sync_ro_regs sync_ro;
> > + char padding[1024];
> > + };
> > + union {
> > + /* read/write guest registers */
> > + struct kvm_sync_rw_regs sync_rw;
> > + char padding[1024];
> > + };
>
> Ah, new patch set. Same comment here. Please give the union a name. Also, I
> still don't understand why we need 2 structs.
Right.
> All we need is a bitmap that says "this field is dirty" and then kernel space
> can decide to ignore it.
Makes sense.
--
error compiling committee.c: too many arguments to function
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