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

[Avi Kivity <avi@redhat.com>]

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.

-- 
error compiling committee.c: too many arguments to function