From: Ashish Kalra <ashish.kalra@amd.com>
To: Borislav Petkov <bp@alien8.de>
Cc: konrad.wilk@oracle.com, hch@lst.de, tglx@linutronix.de,
mingo@redhat.com, hpa@zytor.com, x86@kernel.org, luto@kernel.org,
peterz@infradead.org, dave.hansen@linux-intel.com,
iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
brijesh.singh@amd.com, Thomas.Lendacky@amd.com,
Jon.Grimm@amd.com, rientjes@google.com
Subject: Re: [PATCH v8] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.
Date: Wed, 9 Dec 2020 13:19:46 +0000 [thread overview]
Message-ID: <20201209131946.GA6495@ashkalra_ubuntu_server> (raw)
In-Reply-To: <20201209125442.GC18203@zn.tnic>
On Wed, Dec 09, 2020 at 01:54:42PM +0100, Borislav Petkov wrote:
> On Wed, Dec 09, 2020 at 12:29:07PM +0000, Ashish Kalra wrote:
> > As i mentioned in the main comments above, this cannot be called in
> > mem_encrypt_init() as that breaks reserve_crashkernel() which depends
> > on SWIOTLB buffer size
>
> Please elaborate how does it break.
>
reserve_crashkernel() calls swiotlb_size_or_default() to get SWIOTLB
buffer size and then accordingly allocates low memory for crashkernel.
If SWIOTLB buffer size is adjusted after reserve_crashkernel() and
swiotlb_size_or_default(), then SWIOTLB buffers will overlap the memory
reserved for crashkernel. Hence any SWIOTLB buffer adjustment needs to
be done before or in swiotlb_size_or_default(), but Konrad is not in
favor of modifying swiotlb_size_or_default(), hence this separate
swiotlb_adjust() interface is introduced.
> > and is called before mem_encrypt_init(), therefore, it needs to be
> > called from setup_atch() before reserve_crashkernel().
>
> I know you have your requirements what needs to be called when like all
> the other vendors who want to run stuff early in a particular order but
> our boot init order is a single fragile mess. So this better be done
> right!
>
> Also,
>
> [ 0.016630] software IO TLB: swiotlb_adjust:
> [ 0.017005] reserve_crashkernel:
> [ 0.050523] software IO TLB: swiotlb_init:
>
> this looks strange - we're doing a swiotlb size adjust before init.
>
> It probably makes sense as in: adjust the size before the SWIOTLB is
> initialized so that it uses the correct size but this better be spelled
> out.
>
Yes the adjustment is done before init.
> > I believe that other memory encryption architectures such as s390 are
> > also looking for something similar to be available.
>
> Until you have something more palpable than belief, "let the others
> extend it when they really need it." as I already mentioned.
There is a need to introduce an architecture specific callback
for swiotlb_adjust() because of the following reason :
The sev_active() function is only available to x86, so this will break
other archs, if we use this function in generic swiotlb code.
Therefore, we need arch-specific callback/interface to be invoked from
generic swiotlb code to do the SEV specific actions such as SWIOTLB
buffer size adjustment.
Thanks,
Ashish
next prev parent reply other threads:[~2020-12-09 13:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 23:10 [PATCH v8] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests Ashish Kalra
2020-12-08 22:22 ` Konrad Rzeszutek Wilk
2020-12-08 23:01 ` Borislav Petkov
2020-12-08 23:27 ` Konrad Rzeszutek Wilk
2020-12-08 23:33 ` Borislav Petkov
2020-12-09 11:01 ` Borislav Petkov
2020-12-09 12:29 ` Ashish Kalra
2020-12-09 12:54 ` Borislav Petkov
2020-12-09 13:19 ` Ashish Kalra [this message]
2020-12-09 17:51 ` Borislav Petkov
2020-12-09 19:34 ` Ashish Kalra
2020-12-09 19:43 ` Borislav Petkov
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