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

["Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@linux.intel.com>]

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