Re: [PATCH 5/9] x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest

Vitaly Kuznetsov
2023-06-05T13:01:32Z

Tianyu Lan <ltykernel@gmail.com> writes:

> From: Tianyu Lan <tiala@microsoft.com>
>
> In sev-snp enlightened guest, Hyper-V hypercall needs
> to use vmmcall to trigger vmexit and notify hypervisor
> to handle hypercall request.
>
> There is no x86 SEV SNP feature flag support so far and
> hardware provides MSR_AMD64_SEV register to check SEV-SNP
> capability with MSR_AMD64_SEV_ENABLED bit. ALTERNATIVE can't
> work without SEV-SNP x86 feature flag. May add later when
> the associated flag is introduced.
>
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
> arch/x86/include/asm/mshyperv.h | 44 ++++++++++++++++++++++++---------
> 1 file changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 31c476f4e656..d859d7c5f5e8 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -61,16 +61,25 @@ 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()) {

Would it be possible to redo 'hv_isolation_type_en_snp()' into a static
inline doing static_branch_unlikely() so we avoid function call penalty
here?

> + __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);
> @@ -104,7 +113,13 @@ static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
> u64 hv_status;
>
> #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)
> @@ -149,7 +164,14 @@ static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
> u64 hv_status;
>
> #ifdef CONFIG_X86_64
> - {
> + if (hv_isolation_type_en_snp()) {
> + __asm__ __volatile__("mov %4, %%r8\n"
> + "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,

--
Vitaly