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Subject: Re: [PATCH 03/13] x86/HV: Add new hvcall guest address host
 visibility support
To:     Tianyu Lan <ltykernel@gmail.com>, kys@microsoft.com,
        haiyangz@microsoft.com, sthemmin@microsoft.com, wei.liu@kernel.org,
        decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com,
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        will@kernel.org, davem@davemloft.net, kuba@kernel.org,
        jejb@linux.ibm.com, martin.petersen@oracle.com, arnd@arndb.de,
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        thomas.lendacky@amd.com, brijesh.singh@amd.com, ardb@kernel.org,
        Tianyu.Lan@microsoft.com, rientjes@google.com,
        martin.b.radev@gmail.com, akpm@linux-foundation.org,
        rppt@kernel.org, kirill.shutemov@linux.intel.com,
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        vkuznets@redhat.com, anparri@microsoft.com
References: <20210728145232.285861-1-ltykernel@gmail.com>
 <20210728145232.285861-4-ltykernel@gmail.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <c00e269c-da4c-c703-0182-0221c73a76cc@intel.com>
Date:   Wed, 28 Jul 2021 08:29:41 -0700
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In-Reply-To: <20210728145232.285861-4-ltykernel@gmail.com>
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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.