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@xxxxxxxxxx>
> >>>---
> >>> 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.
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