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

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Message-ID: <1830c3cc-635a-ab59-e217-f48fca8d9cf5@linux.intel.com>
Date:   Thu, 7 Oct 2021 19:16:08 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 09/11] x86/tdx: Add MSR support for TDX guest



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