linux-kernel - RE: [RFC PATCH V2 11/18] Drivers: hv: vmbus: Decrypt vmbus ring buffer

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Date:   Wed, 14 Dec 2022 18:25:51 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "jgross@...e.com" <jgross@...e.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
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CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [RFC PATCH V2 11/18] Drivers: hv: vmbus: Decrypt vmbus ring
 buffer

From: Tianyu Lan <ltykernel@...il.com> Sent: Friday, November 18, 2022 7:46 PM
> 
> The ring buffer is remapped in the hv_ringbuffer_init()
> and it should be with decrypt flag in order to share it
> with hypervisor in sev-snp enlightened guest.

FWIW, the change in this patch is included in Patch 9
in my vTOM-related patch series.

> 
> Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
> ---
>  drivers/hv/ring_buffer.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 59a4aa86d1f3..391995c76be7 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -18,6 +18,7 @@
>  #include <linux/slab.h>
>  #include <linux/prefetch.h>
>  #include <linux/io.h>
> +#include <linux/set_memory.h>
>  #include <asm/mshyperv.h>
> 
>  #include "hyperv_vmbus.h"
> @@ -233,14 +234,18 @@ int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
> 
>  		ring_info->ring_buffer = (struct hv_ring_buffer *)
>  			vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP,
> +				hv_isolation_type_en_snp() ?
> +				pgprot_decrypted(PAGE_KERNEL_NOENC) :
>  				PAGE_KERNEL);

Note that pgprot_decrypted(PAGE_KERNEL_NOENC) can always be
used, as it does nothing in a normal VM.  Its use doesn't need to be
conditional on the isolation type.

> 
> +		if (hv_isolation_type_en_snp())
> +			memset(ring_info->ring_buffer, 0x00, page_cnt * PAGE_SIZE);

My version of the change always does the zero'ing, but only of
the first page, as Hyper-V expects the ring buffer header page to be
clean.  The initial contents of the rest of the ring buffer doesn't
really matter.

> +
>  		kfree(pages_wraparound);
>  		if (!ring_info->ring_buffer)
>  			return -ENOMEM;
>  	}
> 
> -

The above looks like a spurious whitespace change.

>  	ring_info->ring_buffer->read_index =
>  		ring_info->ring_buffer->write_index = 0;
> 
> --
> 2.25.1