Re: [Xen-devel] [PATCH v6 2/4] x86/hvm: Treat non-instruction fetch nested page faults also as read violations

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Tamas K Lengyel [mailto:tamas.lengyel@xxxxxxxxxxxx]
> Sent: Monday, August 11, 2014 7:49 AM
> 
> As pointed out by Jan Beulich in
> http://lists.xen.org/archives/html/xen-devel/2014-08/msg01269.html:
> "Read-modify-write instructions absolutely need to be treated as read
> accesses, yet hardware doesn't guarantee to tell us so (they may surface as
> just write accesses)." This patch addresses the issue in both the VMX and the
> SVM side.
> 
> VMX: Treat all non-instruction fetch violations as read violations (in 
> addition to
> those that were already reported as read violations).

so as a result all the write violations are also treated as read violations 
here? 
it's more than fixing the comment above...

> SVM: Refine the handling to distinguish between read/write and instruction
> fetch access violations.
> 
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/svm/svm.c | 2 +-
>  xen/arch/x86/hvm/vmx/vmx.c | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> index 1f72e19..9531248 100644
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -1404,7 +1404,7 @@ static void svm_do_nested_pgfault(struct vcpu *v,
>      struct p2m_domain *p2m = NULL;
> 
>      struct npfec npfec = {
> -        .read_access = 1, /* All NPFs count as reads */
> +        .read_access = !(pfec & PFEC_insn_fetch),
>          .write_access = !!(pfec & PFEC_write_access),
>          .insn_fetch = !!(pfec & PFEC_insn_fetch)
>      };
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 656ce61..af0ad7c 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -2354,7 +2354,8 @@ static void ept_handle_violation(unsigned long
> qualification, paddr_t gpa)
>      int ret;
>      struct domain *d = current->domain;
>      struct npfec npfec = {
> -        .read_access = !!(qualification & EPT_READ_VIOLATION),
> +        .read_access = !!(qualification & EPT_READ_VIOLATION) ||
> +                        !(qualification & EPT_EXEC_VIOLATION),
>          .write_access = !!(qualification & EPT_WRITE_VIOLATION),
>          .insn_fetch = !!(qualification & EPT_EXEC_VIOLATION)
>      };
> --
> 2.0.1


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