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

[Michael Kelley (LINUX)]

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?

> 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.

>  	}
>  #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");

Same here.  Above 5 lines appear to be changes only in indentation.

>  	}
>  #else
>  	{
> @@ -177,6 +199,7 @@ int hv_map_ioapic_interrupt(int ioapic_id, bool level, int vcpu,
> int vector,
>  		struct hv_interrupt_entry *entry);
>  int hv_unmap_ioapic_interrupt(int ioapic_id, struct hv_interrupt_entry *entry);
>  int hv_set_mem_host_visibility(unsigned long addr, int numpages, bool visible);
> +int hv_snp_boot_ap(int cpu, unsigned long start_ip);

This declaration doesn't seem to belong in this patch.  It should be
in Patch 13 of the series.

> 
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  void hv_ghcb_msr_write(u64 msr, u64 value);
> @@ -191,6 +214,7 @@ static inline void hv_ghcb_terminate(unsigned int set, unsigned
> int reason) {}
>  #endif
> 
>  extern bool hv_isolation_type_snp(void);
> +extern bool hv_isolation_type_en_snp(void);

This declaration seems to be a duplicate that doesn't belong in
this patch.

> 
>  static inline bool hv_is_synic_reg(unsigned int reg)
>  {
> --
> 2.25.1