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From: Michael Ellerman <>
To: Daniel Axtens <>,
	Xianting Tian <>,,,,,
Cc: Xianting Tian <>,,,,
Subject: Re: [PATCH v8 2/3] tty: hvc: pass DMA capable memory to put_chars()
Date: Fri, 20 Aug 2021 22:34:02 +1000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Daniel Axtens <> writes:
> Xianting Tian <> writes:
>> As well known, hvc backend driver(eg, virtio-console) can register its
>> operations to hvc framework. The operations can contain put_chars(),
>> get_chars() and so on.
>> Some hvc backend may do dma in its operations. eg, put_chars() of
>> virtio-console. But in the code of hvc framework, it may pass DMA
>> incapable memory to put_chars() under a specific configuration, which
>> is explained in commit c4baad5029(virtio-console: avoid DMA from stack):
> We could also run into issues on powerpc where Andrew is working on
> adding vmap-stack but the opal hvc driver assumes that it is passed a
> buffer which is not in vmalloc space but in the linear mapping.

The right fix for that is our code that calls opal has to be careful
that it's not passing vmalloc addresses.

We have many cases where we pass stack variables to opal, they'll all
have to be fixed to pass the underlying phyiscal/linear map address. The
opal hvc code will just be one more case of that.


  parent reply	other threads:[~2021-08-20 12:34 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18  8:21 [PATCH v8 0/3] make hvc pass dma capable memory to its backend Xianting Tian
2021-08-18  8:21 ` [PATCH v8 1/3] tty: hvc: use correct dma alignment size Xianting Tian
2021-08-18  8:21 ` [PATCH v8 2/3] tty: hvc: pass DMA capable memory to put_chars() Xianting Tian
2021-08-18 11:03   ` kernel test robot
2021-08-18 17:41   ` kernel test robot
2021-08-20  6:49   ` Daniel Axtens
2021-08-20  8:43     ` Xianting TIan
2021-09-18 12:32       ` Xianting Tian
2021-09-18 12:40         ` Greg KH
2021-09-18 12:47           ` Xianting Tian
2021-08-20 12:34     ` Michael Ellerman [this message]
2021-08-18  8:21 ` [PATCH v8 3/3] virtio-console: remove unnecessary kmemdup() Xianting Tian

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