Re: [PATCH v5 4/5] KVM: x86: emulation: Apply LAM mask when emulating data access in 64-bit mode

[Robert Hoo <robert.hu@linux.intel.com>]

On Fri, 2023-03-03 at 09:08 +0800, Binbin Wu wrote:
> On 3/2/2023 9:16 PM, Robert Hoo wrote:
> > On Thu, 2023-03-02 at 14:41 +0800, Binbin Wu wrote:
> > > __linearize is not the only path the modified LAM canonical check
> > > needed, also some vmexits path should be taken care of, like VMX,
> > > SGX
> > > ENCLS.
> > > 
> > 
> > SGX isn't in this version's implementation's scope, like nested
> > LAM.
> 
> LAM in SGX enclave mode is not the scope of the this version.
> But I think since the capability is exposed to guest, 

I think you can document this or other method to call out this to user.
Even Kernel enabling doesn't include SGX interaction yet, I doubt if
it's that urgent for KVM to do this at this phase.

> need to cover the 
> case if the guest use the supervisor mode pointer

No business with pointer mode here, I think.

>  as the operand of SGX 
> EENCS operations.
> 
> 
> > 
> > > Also the instruction INVLPG, INVPCID should have some special
> > > handling
> > > since LAM is not applied to the memory operand of the two
> > > instruction
> > > according to the LAM spec.
> > 
> > The spec's meaning on these 2 is: LAM masking doesn't apply to
> > their
> > operands (the address), so the behavior is like before LAM feature
> > introduced. No change.
> 
> Yes, LAM are not applied to the 2 instrustions, but the __linearize
> is 
> changed.
> For example, the emulation of invlpg (em_invpg) will also call it.
> So 
> need to handle the case specificlly.
> Can add a flag as the input of linearize to indicate the LAM check
> and 
> untag is needed or not.
> 
No need.

"The INVLPG instruction ...
LAM does not apply to the specified memory address. Thus, in 64-bit
mode, ** if the memory address specified is in non-canonical form then
the INVLPG is the same as a NOP. **

The INVPCID instruction ...
LAM does not apply to the specified memory address, and in 64-bit
mode ** if this memory address is in non-canonical form then the
processor generates a #GP(0) exception. **"

You can double confirm in SDM: Before-and-After LAM introduced, the
behavior hasn't changed. Thus you don't need to worry about these 2
INS's emulations.