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From: Marcelo Tosatti on 11 Jun 2010 16:40
On Fri, Jun 11, 2010 at 07:30:50PM +0800, Lai Jiangshan wrote:
> When ept enabled, current code set shadow_base_present_pte
> including the write bit, thus all pte entries have
> writabe bit, and it means guest os can always
> write to any mapped page (even VMM maps RO pages for
> the guest.)
>
> We always use get_user_pages(write=1), so this bad code does not
> cause any bad result currently.
>
> But it is really bad, so fix it, and we will use RO pages future.
>
> We will set writabe bit when it is really writable (determined by
> the parameters of the set_spte())
>
> Signed-off-by: Lai Jiangshan <laijs(a)cn.fujitsu.com>
> ---
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index fdb18cf..c7565ea 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4365,8 +4365,7 @@ static int __init vmx_init(void)
>
> if (enable_ept) {
> bypass_guest_pf = 0;
> - kvm_mmu_set_base_ptes(VMX_EPT_READABLE_MASK |
> - VMX_EPT_WRITABLE_MASK);
> + kvm_mmu_set_base_ptes(VMX_EPT_READABLE_MASK);
> kvm_mmu_set_mask_ptes(0ull, 0ull, 0ull, 0ull,
> VMX_EPT_EXECUTABLE_MASK);
> kvm_enable_tdp();

You can remove the call to kvm_mmu_set_base_ptes entirely, because
VMX_EPT_READABLE_MASK == PT_PRESENT_MASK.

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From: Avi Kivity on 13 Jun 2010 04:10
On 06/11/2010 10:50 PM, Marcelo Tosatti wrote:
> On Fri, Jun 11, 2010 at 07:30:50PM +0800, Lai Jiangshan wrote:
>
>> When ept enabled, current code set shadow_base_present_pte
>> including the write bit, thus all pte entries have
>> writabe bit, and it means guest os can always
>> write to any mapped page (even VMM maps RO pages for
>> the guest.)
>>
>> We always use get_user_pages(write=1), so this bad code does not
>> cause any bad result currently.
>>
>> But it is really bad, so fix it, and we will use RO pages future.
>>
>> We will set writabe bit when it is really writable (determined by
>> the parameters of the set_spte())
>>
>> Signed-off-by: Lai Jiangshan<laijs(a)cn.fujitsu.com>
>> ---
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index fdb18cf..c7565ea 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -4365,8 +4365,7 @@ static int __init vmx_init(void)
>>
>> if (enable_ept) {
>> bypass_guest_pf = 0;
>> - kvm_mmu_set_base_ptes(VMX_EPT_READABLE_MASK |
>> - VMX_EPT_WRITABLE_MASK);
>> + kvm_mmu_set_base_ptes(VMX_EPT_READABLE_MASK);
>> kvm_mmu_set_mask_ptes(0ull, 0ull, 0ull, 0ull,
>> VMX_EPT_EXECUTABLE_MASK);
>> kvm_enable_tdp();
>>
> You can remove the call to kvm_mmu_set_base_ptes entirely, because
> VMX_EPT_READABLE_MASK == PT_PRESENT_MASK.
>

We can leave that to a later patch which removes kvm_mmu_set_base_ptes()
entirely.

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

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