Re: [RFC PATCH V2 06/18] x86/hyperv: Use vmmcall to implement hvcall in sev-snp enlightened guest

[Tianyu Lan]

On 12/14/2022 1:19 AM, Michael Kelley (LINUX) wrote:
> From: Tianyu Lan <ltykernel@xxxxxxxxx> Sent: Friday, November 18, 2022 7:46 PM
> > In sev-snp enlightened guest, hvcall needs to use vmmcall to trigger
>
> What does "hvcall" refer to here?  Is this a Hyper-V hypercall, or just
> a generic hypervisor call?

It's should be Hyper-V hypercall. Will make it accurate in the next
version. Thanks for reminder.

> > vmexit and notify hypervisor to handle hypercall request.
> >
> > Signed-off-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/mshyperv.h | 66 ++++++++++++++++++++++-----------
> >   1 file changed, 45 insertions(+), 21 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> > index 9b8c3f638845..28d5429e33c9 100644
> > --- a/arch/x86/include/asm/mshyperv.h
> > +++ b/arch/x86/include/asm/mshyperv.h
> > @@ -45,16 +45,25 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
> >   	u64 hv_status;
> >
> >   #ifdef CONFIG_X86_64
> > -	if (!hv_hypercall_pg)
> > -		return U64_MAX;
> > +	if (hv_isolation_type_en_snp()) {
> > +		__asm__ __volatile__("mov %4, %%r8\n"
> > +				"vmmcall"
> > +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > +				"+c" (control), "+d" (input_address)
> > +				:  "r" (output_address)
> > +				: "cc", "memory", "r8", "r9", "r10", "r11");
> > +	} else {
> > +		if (!hv_hypercall_pg)
> > +			return U64_MAX;
> >
> > -	__asm__ __volatile__("mov %4, %%r8\n"
> > -			     CALL_NOSPEC
> > -			     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > -			       "+c" (control), "+d" (input_address)
> > -			     :  "r" (output_address),
> > -				THUNK_TARGET(hv_hypercall_pg)
> > -			     : "cc", "memory", "r8", "r9", "r10", "r11");
> > +		__asm__ __volatile__("mov %4, %%r8\n"
> > +				CALL_NOSPEC
> > +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > +				"+c" (control), "+d" (input_address)
> > +				:  "r" (output_address),
> > +					THUNK_TARGET(hv_hypercall_pg)
> > +				: "cc", "memory", "r8", "r9", "r10", "r11");
> > +	}
> >   #else
> >   	u32 input_address_hi = upper_32_bits(input_address);
> >   	u32 input_address_lo = lower_32_bits(input_address);
> > @@ -82,12 +91,18 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
> >   	u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
> >
> >   #ifdef CONFIG_X86_64
> > -	{
> > +	if (hv_isolation_type_en_snp()) {
> > +		__asm__ __volatile__(
> > +				"vmmcall"
> > +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > +				"+c" (control), "+d" (input1)
> > +				:: "cc", "r8", "r9", "r10", "r11");
> > +	} else {
> >   		__asm__ __volatile__(CALL_NOSPEC
> > -				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > -				       "+c" (control), "+d" (input1)
> > -				     : THUNK_TARGET(hv_hypercall_pg)
> > -				     : "cc", "r8", "r9", "r10", "r11");
> > +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > +				"+c" (control), "+d" (input1)
> > +				: THUNK_TARGET(hv_hypercall_pg)
> > +				: "cc", "r8", "r9", "r10", "r11");
>
> The above 4 lines appear to just have changes in indentation.  Maybe
> there's value in having the same indentation as the new code you've
> added, so I won't object if you want to keep the changes.

OK. Will update in the next version.

> >   	}
> >   #else
> >   	{
> > @@ -113,14 +128,21 @@ static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
> >   	u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
> >
> >   #ifdef CONFIG_X86_64
> > -	{
> > +	if (hv_isolation_type_en_snp()) {
> >   		__asm__ __volatile__("mov %4, %%r8\n"
> > -				     CALL_NOSPEC
> > -				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > -				       "+c" (control), "+d" (input1)
> > -				     : "r" (input2),
> > -				       THUNK_TARGET(hv_hypercall_pg)
> > -				     : "cc", "r8", "r9", "r10", "r11");
> > +				"vmmcall"
> > +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > +				"+c" (control), "+d" (input1)
> > +				: "r" (input2)
> > +				: "cc", "r8", "r9", "r10", "r11");
> > +	} else {
> > +		__asm__ __volatile__("mov %4, %%r8\n"
> > +				CALL_NOSPEC
> > +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> > +				"+c" (control), "+d" (input1)
> > +				: "r" (input2),
> > +				THUNK_TARGET(hv_hypercall_pg)
> > +				: "cc", "r8", "r9", "r10", "r11");