From: Dave Hansen <dave.hansen@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Mel Gorman <mgorman@techsingularity.net>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrea Arcangeli <aarcange@redhat.com>,
Dan Williams <dan.j.williams@intel.com>,
David Hildenbrand <david@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Raj, Ashok" <ashok.raj@intel.com>
Subject: Re: [RFC PATCH 0/4] mm: Add PG_zero support
Date: Mon, 13 Apr 2020 08:14:32 -0700 [thread overview]
Message-ID: <7a064e81-6bc1-b3e7-5f82-292ffa392058@intel.com> (raw)
In-Reply-To: <20200413084915.1bae0007@w520.home>
On 4/13/20 7:49 AM, Alex Williamson wrote:
>> VFIO's unconditional page pinning is the real problem here IMNHO. They
>> don't *really* need to pin the memory. We just don't have good
>> paravirtualized IOMMU support or want to pay the runtime cost for
>> pin/unpin operations. You *could* totally have speedy VM startup if
>> only the pages being accessed or having DMA performed to them were
>> allocated. But, the hacks that are in place mean that everything must
>> be pinned.
> Maybe in an SEV or Secure Boot environment we can assume the VM guest
> OS uses the IOMMU exclusively for DMA, but otherwise the IOMMU is
> optional (at least for x86, other archs do require IOMMU support
> afaik). Therefore, how would we know which pages to pin when there are
> only limited configs where we might be able to lean on the vIOMMU to
> this extent? Thanks,
You can delay pinning until the device is actually used. That should be
late enough for the host to figure out whether a paravirtualized IOMMU
is in place.
next prev parent reply other threads:[~2020-04-13 15:14 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-12 9:07 [RFC PATCH 0/4] mm: Add PG_zero support liliangleo
2020-04-13 1:43 ` Dave Hansen
2020-04-13 14:49 ` Alex Williamson
2020-04-13 15:14 ` Dave Hansen [this message]
2020-04-13 15:25 ` Raj, Ashok
2020-04-13 15:47 ` Alex Williamson
2020-04-13 16:43 ` Dave Hansen
2020-04-14 12:01 ` David Hildenbrand
2020-04-14 15:07 ` Alexander Duyck
2020-04-14 15:40 ` Daniel Jordan
2020-04-14 15:44 ` David Hildenbrand
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