Re: [PATCH 15/24] KVM: x86 emulator: Provide more callbacks for x86 emulator.

[Gleb Natapov <gleb@redhat.com>]

On Tue, Mar 09, 2010 at 07:22:51PM +0200, Avi Kivity wrote:
> On 03/09/2010 06:25 PM, Gleb Natapov wrote:
> >On Tue, Mar 09, 2010 at 04:43:59PM +0200, Avi Kivity wrote:
> >>On 03/09/2010 04:09 PM, Gleb Natapov wrote:
> >>>Provide get_cached_descriptor(), set_cached_descriptor(),
> >>>get_segment_selector(), set_segment_selector(), get_gdt(),
> >>>write_std() callbacks.
> >>>
> >>>Signed-off-by: Gleb Natapov<gleb@redhat.com>
> >>>---
> >>>  arch/x86/include/asm/kvm_emulate.h |   16 +++++
> >>>  arch/x86/kvm/x86.c                 |  130 +++++++++++++++++++++++++++++++----
> >>>  2 files changed, 131 insertions(+), 15 deletions(-)
> >>>
> >>>diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> >>>index 032d02f..e881618 100644
> >>>--- a/arch/x86/include/asm/kvm_emulate.h
> >>>+++ b/arch/x86/include/asm/kvm_emulate.h
> >>>@@ -63,6 +63,15 @@ struct x86_emulate_ops {
> >>>  			unsigned int bytes, struct kvm_vcpu *vcpu, u32 *error);
> >>>
> >>>  	/*
> >>>+	 * write_std: Write bytes of standard (non-emulated/special) memory.
> >>>+	 *            Used for descriptor writing.
> >>>+	 *  @addr:  [IN ] Linear address to which to write.
> >>>+	 *  @val:   [OUT] Value write to memory, zero-extended to 'u_long'.
> >>>+	 *  @bytes: [IN ] Number of bytes to write to memory.
> >>>+	 */
> >>>+	int (*write_std)(unsigned long addr, void *val,
> >>>+			 unsigned int bytes, struct kvm_vcpu *vcpu, u32 *error);
> >>Descriptor writes need an atomic kvm_set_guest_bit(), no?
> >>
> >It is? atomic against what? Current code just write whole descriptor
> >using write_std().
> 
> These are accessed bit changes, and are done atomically in the same
> way as a page table walk sets the accessed and dirty bit.
> Presumably the atomic operation is to allow the kernel to scan
> segments and swap them out if they are not used.
> 
We can use cmpxchg callback for that, no?

--
			Gleb.