Re: [PATCH v8 09/11] x86/tdx: Add MSR support for TDX guest

[Kuppuswamy, Sathyanarayanan]

On 10/6/21 12:49 PM, Josh Poimboeuf wrote:
> On Mon, Oct 04, 2021 at 07:52:03PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> > index 3d0416515506..062ac4720434 100644
> > --- a/arch/x86/kernel/tdx.c
> > +++ b/arch/x86/kernel/tdx.c
> > @@ -110,6 +110,41 @@ static __cpuidle void tdx_safe_halt(void)
> >   	_tdx_halt(irq_disabled, do_sti);
> >   }
> >   
> > +static u64 tdx_read_msr_safe(unsigned int msr, int *err)
>
> Here the kernel convention would probably be to return the error and
> make 'val' an argument:
>
> static int tdx_read_msr_safe(unsigned int msr, u64 *val)

Agree. I will fix this in next version.

> > +{
> > +	struct tdx_hypercall_output out = {0};
> > +	u64 ret;
> > +
> > +	/*
> > +	 * Emulate the MSR read via hypercall. More info about ABI
> > +	 * can be found in TDX Guest-Host-Communication Interface
> > +	 * (GHCI), sec titled "TDG.VP.VMCALL<Instruction.RDMSR>".
> > +	 */
> > +	ret = _tdx_hypercall(EXIT_REASON_MSR_READ, msr, 0, 0, 0, &out);
> > +
> > +	*err = ret ? -EIO : 0;
> > +
> > +	return out.r11;
> > +}
> > +
> > +static int tdx_write_msr_safe(unsigned int msr, unsigned int low,
> > +			      unsigned int high)
> > +{
> > +	u64 ret;
> > +
> > +	WARN_ON_ONCE(tdx_is_context_switched_msr(msr));
>
> This fails to build, tdx_is_context_switched_msr() is missing.
>
> > @@ -136,19 +171,33 @@ unsigned long tdx_get_ve_info(struct ve_info *ve)
> >   int tdx_handle_virtualization_exception(struct pt_regs *regs,
> >   					struct ve_info *ve)
> >   {
> > +	unsigned long val;
> > +	int ret = 0;
> > +
> >   	switch (ve->exit_reason) {
> >   	case EXIT_REASON_HLT:
> >   		tdx_halt();
> >   		break;
> > +	case EXIT_REASON_MSR_READ:
> > +		val = tdx_read_msr_safe(regs->cx, (unsigned int *)&ret);
>
> Why the 'unsigned int *' cast?
>
> Also, 'val' should have the same type as the one returned by
> tdx_read_msr_safe().  (Though it technically doesn't matter here.)

I will change val type to u64. It will not need any casting.

>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer