Re: [PATCH] KVM: VMX: Judge MMIO based on PFN rather than HVA in EPT violation

[Marcelo Tosatti <mtosatti@redhat.com>]

Hi Sheng,

On Tue, Feb 10, 2009 at 05:43:41PM +0800, Sheng Yang wrote:
> One page can be unmapped from userspace, then HVA seems legal, but in fact,
> PFN is illegal.
> 
> Signed-off-by: Sheng Yang <sheng@linux.intel.com>
> ---
>  arch/x86/kvm/vmx.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9913a1d..a4fa1b5 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3061,7 +3061,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>  	u64 exit_qualification;
>  	enum emulation_result er;
>  	gpa_t gpa;
> -	unsigned long hva;
> +	pfn_t pfn;
>  	int gla_validity;
>  	int r;
>  
> @@ -3086,8 +3086,8 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>  	}
>  
>  	gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
> -	hva = gfn_to_hva(vcpu->kvm, gpa >> PAGE_SHIFT);
> -	if (!kvm_is_error_hva(hva)) {
> +	pfn = gfn_to_pfn(vcpu->kvm, gpa >> PAGE_SHIFT);
> +	if (!is_error_pfn(pfn)) {
>  		r = kvm_mmu_page_fault(vcpu, gpa & PAGE_MASK, 0);
>  		if (r < 0) {
>  			printk(KERN_ERR "EPT: Not enough memory!\n");

Forgot to drop the additional reference acquired by gfn_to_pfn ?

Hum, gfn_to_hva assumes the slot information is accurate, which is not
the case if you simply munmap a page in the middle of a slot... we
should provide a helper in userspace, and make sure nothing bad can
happen otherwise. 

Anyway, why don't you just let kvm_mmu_page_fault handle instruction
emulation instead of opencoding it in handle_ept_violation ?