Re: [PATCH v3 10/14] x86/vmx: move declarations used only by vmx code from vmx.h to private headers

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/02/2023 6:50 pm, Xenia Ragiadakou wrote:
> Create two new private headers in arch/x86/hvm/vmx called vmx.h and pi.h.
> Move all the definitions and declarations that are used solely by vmx code
> into the private vmx.h, apart from the ones related to posted interrupts that
> are moved into pi.h.
>
> EPT related declarations and definitions stay in asm/hvm/vmx/vmx.h because
> they are used in arch/x86/mm and drivers/passthrough/vtd.
>
> Also, __vmread(), used in arch/x86/cpu, and consequently the opcodes stay in
> asm/hvm/vmx/vmx.h.

Every time I read the vpmu code, I get increasingly sad.

That is dangerously unsafe, and comes with a chance of exploding completely.

That __vmread() is in NMI context, which means `current` isn't safe to
deference (we might hit in the middle of a context switch), and more
generally there's no guarantee that the loaded VMCS is the one
associated with `current` (we might hit in the middle of a remote VMCS
access).

vpmu is generally not supported, and BTS needs further custom enablement
because it is only useable with a custom bus analyser.


The __vmread() needs deleting - its absolutely not safe to say.

I'm tempted to hardwire the return 0, and punt the problem to whomever
next uses BTS.

Alternatively, MSR_DBGCTL needs wiring into the hvm_get_reg()
infrastructure, but I'm not convinced this will actually work in either
of the two problem cases above, hence preferring the previous option.

Thoughts?

~Andrew