RE: [PATCH 5/6] x86/hyperv: Support hypercalls for TDX guests

[Dexuan Cui]

> From: Dave Hansen <dave.hansen@xxxxxxxxx>
> Sent: Monday, November 28, 2022 1:15 PM
> [...]
> This is the point where the maintainer gets a wee bit grumpy.  The page
> I just pointed you to (twice) has this nice quote:
> 
> 	If the hypercall involves no input or output parameters, the
> 	hypervisor ignores the corresponding GPA pointer.
> 
> So, bravo to your colleagues who nicely documented this.  But,
> unfortunately, you didn't take advantage of their great documentation.
> Instead, you made me search for it to provide actual facts to combat the
> weak conjecture you offered above.

Sorry, I should really have read the document before starting to conjecture...

> > The above is just my conjecture. I don't know how exactly Hyper-V works.
> 
> I do!  I literally Googled "HV HYPERCALL FAST BIT" and the first page
> that came up told me all I needed to know.
> 
> I could be merrily merging your patches.  But, instead, I'm reading
> documentation that can be trivially found and repeatedly regurgitating it.
> 
> Please, slow down.  Take some time to answer emails and do it more
> deliberately.  This isn't a race.

Thanks, I learn a lesson. Hopefully the below looks good enough. 

Compared to the earlier version, the only changes are: 1) simplified the
change in hv_do_hypercall(); 2) added a comment before the function.

BTW, I can't post the v2 patchset right now, as I'm waiting for Kirill to
expand __tdx_hypercall() first:
https://lwn.net/ml/linux-kernel/SA1PR21MB1335EEEC1DE4CB42F6477A5EBF0C9@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
I'm also thinking about how to properly address the vmalloc
issue with tdx_enc_status_changed().

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 70170049be2c..41395891d112 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -242,6 +242,20 @@ bool hv_isolation_type_tdx(void)
 {
        return static_branch_unlikely(&isolation_type_tdx);
 }
+
+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
+{
+       struct tdx_hypercall_args args = { };
+
+       args.r10 = control;
+       args.rdx = param1;
+       args.r8  = param2;
+
+       (void)__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT);
+
+       return args.r11;
+}
+EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
 #endif

 /*
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 9cc6db45c3bc..055b6fb8941f 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -10,6 +10,7 @@
 #include <asm/nospec-branch.h>
 #include <asm/paravirt.h>
 #include <asm/mshyperv.h>
+#include <asm/coco.h>

 union hv_ghcb;

@@ -39,6 +40,12 @@ int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
 int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
 int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);

+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
+
+/*
+ * If the hypercall involves no input or output parameters, the hypervisor
+ * ignores the corresponding GPA pointer.
+ */
 static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
 {
        u64 input_address = input ? virt_to_phys(input) : 0;
@@ -46,6 +53,10 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
        u64 hv_status;

 #ifdef CONFIG_X86_64
+       if (hv_isolation_type_tdx())
+               return hv_tdx_hypercall(control,
+                                   cc_mkdec(input_address),
+                                   cc_mkdec(output_address));
        if (!hv_hypercall_pg)
                return U64_MAX;

@@ -83,6 +94,9 @@ 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_tdx())
+               return hv_tdx_hypercall(control, input1, 0);
+
        {
                __asm__ __volatile__(CALL_NOSPEC
                                     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
@@ -114,6 +128,9 @@ 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_tdx())
+               return hv_tdx_hypercall(control, input1, input2);
+
        {
                __asm__ __volatile__("mov %4, %%r8\n"
                                     CALL_NOSPEC