Re: [PATCH 03/13] x86/HV: Add new hvcall guest address host visibility support

[Dave Hansen <dave.hansen@xxxxxxxxx>]

On 7/28/21 7:52 AM, Tianyu Lan wrote:
> @@ -1986,7 +1988,9 @@ static int __set_memory_enc_dec(unsigned long addr, int 
> numpages, bool enc)
>       int ret;
>  
>       /* Nothing to do if memory encryption is not active */
> -     if (!mem_encrypt_active())
> +     if (hv_is_isolation_supported())
> +             return hv_set_mem_enc(addr, numpages, enc);
> +     else if (!mem_encrypt_active())
>               return 0;

__set_memory_enc_dec() is turning into a real mess.  SEV, TDX and now
Hyper-V are messing around in here.

It doesn't help that these additions are totally uncommented.  Even
worse is that hv_set_mem_enc() was intentionally named "enc" when it
presumably has nothing to do with encryption.

This needs to be refactored.  The current __set_memory_enc_dec() can
become __set_memory_enc_pgtable().  It gets used for the hypervisors
that get informed about "encryption" status via page tables: SEV and TDX.

Then, rename hv_set_mem_enc() to hv_set_visible_hcall().  You'll end up
with:

int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
{
        if (hv_is_isolation_supported())
                return hv_set_visible_hcall(...);

        if (mem_encrypt_active() || ...)
                return __set_memory_enc_pgtable();

        /* Nothing to do */
        return 0;
}

That tells the story pretty effectively, in code.

> +int hv_set_mem_enc(unsigned long addr, int numpages, bool enc)
> +{
> +     return hv_set_mem_host_visibility((void *)addr,
> +                     numpages * HV_HYP_PAGE_SIZE,
> +                     enc ? VMBUS_PAGE_NOT_VISIBLE
> +                     : VMBUS_PAGE_VISIBLE_READ_WRITE);
> +}

I know this is off in Hyper-V code, but this just makes my eyes bleed.
I'd much rather see something which is less compact but readable.

> +/* Hyper-V GPA map flags */
> +#define      VMBUS_PAGE_NOT_VISIBLE          0
> +#define      VMBUS_PAGE_VISIBLE_READ_ONLY    1
> +#define      VMBUS_PAGE_VISIBLE_READ_WRITE   3

That looks suspiciously like an enum.