Re: [PATCH 3/6] Emulator: Inject #PF when page was not found

2009-05-18 Thread Alexander Graf 


On 17.05.2009, at 22:58, Avi Kivity wrote:


Alexander Graf wrote:


I can't think why it was done for writes.  Normally, a guest page  
fault would be trapped and reflected a long time before emulation,  
in FNAME(page_fault)(), after walk_addr().


Can you give some details on the situation?  What instruction was  
executed, and why kvm tried to emulate it?


I remember it was something about accessing the apic with npt.  
Maybe the real problem was the restricted bit checking that made  
the emulated instruction behave differently from the real mmu.


The apic should not be mapped by Hyper-V's shadow page tables, so  
this should have been handled by page_fault().


I think I only had to include this to find out that the restricted bit  
was checked for, so I got a blue screen in the guest :-).

Hyper-V works fine without this patch on NPT.

Alex
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Re: [PATCH 3/6] Emulator: Inject #PF when page was not found

2009-05-17 Thread Avi Kivity 

Alexander Graf wrote:

If we couldn't find a page on read_emulated, it might be a good
idea to tell the guest about that and inject a #PF.

We do the same already for write faults. I don't know why it was
not implemented for reads.

  


I can't think why it was done for writes.  Normally, a guest page fault 
would be trapped and reflected a long time before emulation, in 
FNAME(page_fault)(), after walk_addr().


Can you give some details on the situation?  What instruction was 
executed, and why kvm tried to emulate it?


(I guess it depends on the relative priority of svm instruction 
intercepts and the page fault intercept?)


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Re: [PATCH 3/6] Emulator: Inject #PF when page was not found

2009-05-17 Thread Alexander Graf 


On 17.05.2009, at 21:59, Avi Kivity a...@redhat.com wrote:


Alexander Graf wrote:

If we couldn't find a page on read_emulated, it might be a good
idea to tell the guest about that and inject a #PF.

We do the same already for write faults. I don't know why it was
not implemented for reads.




I can't think why it was done for writes.  Normally, a guest page  
fault would be trapped and reflected a long time before emulation,  
in FNAME(page_fault)(), after walk_addr().


Can you give some details on the situation?  What instruction was  
executed, and why kvm tried to emulate it?


I remember it was something about accessing the apic with npt. Maybe  
the real problem was the restricted bit checking that made the  
emulated instruction behave differently from the real mmu.


I really need to start writing down why I did things when doing them :).

I can recheck if it still breaks without the inject.

Alex




(I guess it depends on the relative priority of svm instruction  
intercepts and the page fault intercept?)


--
Do not meddle in the internals of kernels, for they are subtle and  
quick to panic.



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Re: [PATCH 3/6] Emulator: Inject #PF when page was not found

2009-05-17 Thread Avi Kivity 

Alexander Graf wrote:


I can't think why it was done for writes.  Normally, a guest page 
fault would be trapped and reflected a long time before emulation, in 
FNAME(page_fault)(), after walk_addr().


Can you give some details on the situation?  What instruction was 
executed, and why kvm tried to emulate it?


I remember it was something about accessing the apic with npt. Maybe 
the real problem was the restricted bit checking that made the 
emulated instruction behave differently from the real mmu.


The apic should not be mapped by Hyper-V's shadow page tables, so this 
should have been handled by page_fault().


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panic.

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[PATCH 3/6] Emulator: Inject #PF when page was not found

2009-05-15 Thread Alexander Graf 
If we couldn't find a page on read_emulated, it might be a good
idea to tell the guest about that and inject a #PF.

We do the same already for write faults. I don't know why it was
not implemented for reads.

Signed-off-by: Alexander Graf ag...@suse.de
---
 arch/x86/kvm/x86.c |7 +--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5fcde2c..5aa1219 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2131,10 +2131,13 @@ static int emulator_read_emulated(unsigned long addr,
goto mmio;
 
if (kvm_read_guest_virt(addr, val, bytes, vcpu)
-   == X86EMUL_CONTINUE)
+   == X86EMUL_CONTINUE) {
return X86EMUL_CONTINUE;
-   if (gpa == UNMAPPED_GVA)
+   }
+   if (gpa == UNMAPPED_GVA) {
+   kvm_inject_page_fault(vcpu, addr, 0);
return X86EMUL_PROPAGATE_FAULT;
+   }
 
 mmio:
/*
-- 
1.6.0.2

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Re: [PATCH 3/6] Emulator: Inject #PF when page was not found

2009-05-15 Thread Joerg Roedel 
On Fri, May 15, 2009 at 10:22:17AM +0200, Alexander Graf wrote:
 If we couldn't find a page on read_emulated, it might be a good
 idea to tell the guest about that and inject a #PF.
 
 We do the same already for write faults. I don't know why it was
 not implemented for reads.

Have you checked that the emulator will never ever do speculative reads?
This may be the reason why the fault was not injected here.

 
 Signed-off-by: Alexander Graf ag...@suse.de
 ---
  arch/x86/kvm/x86.c |7 +--
  1 files changed, 5 insertions(+), 2 deletions(-)
 
 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
 index 5fcde2c..5aa1219 100644
 --- a/arch/x86/kvm/x86.c
 +++ b/arch/x86/kvm/x86.c
 @@ -2131,10 +2131,13 @@ static int emulator_read_emulated(unsigned long addr,
   goto mmio;
  
   if (kvm_read_guest_virt(addr, val, bytes, vcpu)
 - == X86EMUL_CONTINUE)
 + == X86EMUL_CONTINUE) {
   return X86EMUL_CONTINUE;
 - if (gpa == UNMAPPED_GVA)
 + }
 + if (gpa == UNMAPPED_GVA) {
 + kvm_inject_page_fault(vcpu, addr, 0);
   return X86EMUL_PROPAGATE_FAULT;
 + }
  
  mmio:
   /*
 -- 
 1.6.0.2
 
 

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