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

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Date:   Wed, 28 Jul 2021 08:29:41 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tianyu Lan <ltykernel@...il.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
        jgross@...e.com, sstabellini@...nel.org, joro@...tes.org,
        will@...nel.org, davem@...emloft.net, kuba@...nel.org,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, arnd@...db.de,
        hch@....de, m.szyprowski@...sung.com, robin.murphy@....com,
        thomas.lendacky@....com, brijesh.singh@....com, ardb@...nel.org,
        Tianyu.Lan@...rosoft.com, rientjes@...gle.com,
        martin.b.radev@...il.com, akpm@...ux-foundation.org,
        rppt@...nel.org, kirill.shutemov@...ux.intel.com,
        aneesh.kumar@...ux.ibm.com, krish.sadhukhan@...cle.com,
        saravanand@...com, xen-devel@...ts.xenproject.org,
        pgonda@...gle.com, david@...hat.com, keescook@...omium.org,
        hannes@...xchg.org, sfr@...b.auug.org.au,
        michael.h.kelley@...rosoft.com
Cc:     iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, netdev@...r.kernel.org,
        vkuznets@...hat.com, anparri@...rosoft.com
Subject: Re: [PATCH 03/13] x86/HV: Add new hvcall guest address host
 visibility support

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.