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SubjectRe: [PATCH v4 02/14] X86/nVMX: handle_vmptrld: Copy the VMCS12 directly from guest memory
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On 03.12.18 10:30, KarimAllah Ahmed wrote:
> Copy the VMCS12 directly from guest memory instead of the map->copy->unmap
> sequence. This also avoids using kvm_vcpu_gpa_to_page() and kmap() which
> assumes that there is a "struct page" for guest memory.
>
> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> ---
> v3 -> v4:
> - Return VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID on failure (jmattson@)
> v1 -> v2:
> - Massage commit message a bit.
> ---
> arch/x86/kvm/vmx.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index b84f230..75817cb 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -9301,20 +9301,22 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
> return 1;
>
> if (vmx->nested.current_vmptr != vmptr) {
> - struct vmcs12 *new_vmcs12;
> - struct page *page;
> - page = kvm_vcpu_gpa_to_page(vcpu, vmptr);
> - if (is_error_page(page))
> - return nested_vmx_failInvalid(vcpu);
> + struct vmcs12 *new_vmcs12 = (struct vmcs12 *)__get_free_page(GFP_KERNEL);
> +
> + if (!new_vmcs12 ||
> + kvm_read_guest(vcpu->kvm, vmptr, new_vmcs12,
> + sizeof(*new_vmcs12))) {
> + free_page((unsigned long)new_vmcs12);
> + return nested_vmx_failValid(vcpu,
> + VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID);
> + }

If we fail to read, VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID seems t be
the right thing to do (I remember that reading from non-existent memory
returns all 1's).

I somewhat dislike that we are converting -ENOMEM to
VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID. Isn't there a way we can
report -ENOMEM to user space? (or do we really want to avoid crashing
the guest here? if so, comment + print a warning or something like that?)

>
> - new_vmcs12 = kmap(page);
> if (new_vmcs12->hdr.revision_id != VMCS12_REVISION ||
> (new_vmcs12->hdr.shadow_vmcs &&
> !nested_cpu_has_vmx_shadow_vmcs(vcpu))) {
> - kunmap(page);
> - kvm_release_page_clean(page);
> + free_page((unsigned long)new_vmcs12);
> return nested_vmx_failValid(vcpu,
> - VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID);
> + VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID);
> }
>
> nested_release_vmcs12(vcpu);
> @@ -9324,9 +9326,7 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
> * cached.
> */
> memcpy(vmx->nested.cached_vmcs12, new_vmcs12, VMCS12_SIZE);
> - kunmap(page);
> - kvm_release_page_clean(page);
> -
> + free_page((unsigned long)new_vmcs12);
> set_current_vmptr(vmx, vmptr);
> }
>
>


--

Thanks,

David / dhildenb

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