On 30/10/2018 08:06, Tian, Kevin wrote:
>> From: Sergey Dyasli [mailto:sergey.dya...@citrix.com]
>> Sent: Friday, October 12, 2018 11:28 PM
>>
>> The size of Xen's virtual vmcs region is 4096 bytes. Correctly report
>> it to the guest in case when VMCS shadowing is not available instead of
>> providing H/W value (which is usually smaller).
>
> what is the problem of reporting smaller size even when actual
> size is 4096? is L1 expected to access the portion beyond h/w
> reported size?
>
Here's the code snippet from kvm-unit-tests:
vmcs[0]->hdr.revision_id = basic.revision;
assert(!vmcs_clear(vmcs[0]));
assert(!make_vmcs_current(vmcs[0]));
set_all_vmcs_fields(0x86);
assert(!vmcs_clear(vmcs[0]));
memcpy(vmcs[1], vmcs[0], basic.size);
assert(!make_vmcs_current(vmcs[1]));
report("test vmclear flush (current VMCS)",
check_all_vmcs_fields(0x86));
set_all_vmcs_fields() vmwrites almost 4k, but memcpy() copies only 1024
bytes and vmreads get incorrect values.
>>
>> Signed-off-by: Sergey Dyasli <sergey.dya...@citrix.com>
>> ---
>> xen/arch/x86/hvm/vmx/vvmx.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c
>> b/xen/arch/x86/hvm/vmx/vvmx.c
>> index 8b691bfc04..2c2ba36d94 100644
>> --- a/xen/arch/x86/hvm/vmx/vvmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
>> @@ -2064,6 +2064,14 @@ int nvmx_msr_read_intercept(unsigned int msr,
>> u64 *msr_content)
>> data = (host_data & (~0ul << 32)) |
>> (vmcs->vmcs_revision_id & 0x7fffffff);
>> unmap_domain_page(vmcs);
>> +
>> + if ( !cpu_has_vmx_vmcs_shadowing )
>> + {
>> + /* Report vmcs_region_size as 4096 */
>> + data &= ~VMX_BASIC_VMCS_SIZE_MASK;
>> + data |= 1ULL << 44;
>> + }
>> +
>> break;
>> }
>> case MSR_IA32_VMX_PINBASED_CTLS:
>> --
>> 2.17.1
>
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