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From:   "Reshetova, Elena" <elena.reshetova@intel.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
CC:     Andi Kleen <ak@linux.intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        Kuppuswamy Sathyanarayanan 
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Subject: RE: [PATCH v5 12/16] PCI: Add pci_iomap_host_shared(),
 pci_iomap_host_shared_range()
Thread-Topic: [PATCH v5 12/16] PCI: Add pci_iomap_host_shared(),
 pci_iomap_host_shared_range()
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Date:   Thu, 14 Oct 2021 12:33:49 +0000
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> On Thu, Oct 14, 2021 at 07:27:42AM +0000, Reshetova, Elena wrote:
> > > On Thu, Oct 14, 2021 at 06:32:32AM +0000, Reshetova, Elena wrote:
> > > > > On Tue, Oct 12, 2021 at 06:36:16PM +0000, Reshetova, Elena wrote:
> > > > > > > The 5.15 tree has something like ~2.4k IO accesses (including=
 MMIO and
> > > > > > > others) in init functions that also register drivers (thanks =
Elena for
> > > > > > > the number)
> > > > > >
> > > > > > To provide more numbers on this. What I can see so far from a s=
match-
> based
> > > > > > analysis, we have 409 __init style functions (.probe & builtin/=
module_
> > > > > > _platform_driver_probe excluded) for 5.15 with allyesconfig.
> > > > >
> > > > > I don't think we care about allyesconfig at all though.
> > > > > Just don't do that.
> > > > > How about allmodconfig? This is closer to what distros actually d=
o.
> > > >
> > > > It does not make any difference really for the content of the /driv=
ers/*:
> > > > gives 408 __init style functions doing IO (.probe & builtin/module_
> > > > > > _platform_driver_probe excluded) for 5.15 with allmodconfig:
> > > >
> > > > ['doc200x_ident_chip',
> > > > 'doc_probe', 'doc2001_init', 'mtd_speedtest_init',
> > > > 'mtd_nandbiterrs_init', 'mtd_oobtest_init', 'mtd_pagetest_init',
> > > > 'tort_init', 'mtd_subpagetest_init', 'fixup_pmc551',
> > > > 'doc_set_driver_info', 'init_amd76xrom', 'init_l440gx',
> > > > 'init_sc520cdp', 'init_ichxrom', 'init_ck804xrom', 'init_esb2rom',
> > > > 'probe_acpi_namespace_devices', 'amd_iommu_init_pci', 'state_next',
> > > > 'arm_v7s_do_selftests', 'arm_lpae_run_tests', 'init_iommu_one',
> > >
> > > Um. ARM? Which architecture is this build for?
> >
> > The list of smatch IO findings is built for x86, but the smatch cross f=
unction
> > database covers all archs, so when queried for all potential function c=
allers,
> > it would show non x86 arch call chains also.
> >
> > Here is the original x86 finding and call chain for the 'arm_v7s_do_sel=
ftests':
> >
> >   Detected low-level IO from arm_v7s_do_selftests in fun
> > __iommu_queue_command_sync
> >
> > drivers/iommu/amd/iommu.c:1025 __iommu_queue_command_sync() error:
> > {15002074744551330002}
> >     'check_host_input' read from the host using function 'readl' to a
> > member of the structure 'iommu->cmd_buf_head';
> >
> > __iommu_queue_command_sync()
> >   iommu_completion_wait()
> >     amd_iommu_domain_flush_complete()
> >       iommu_v1_map_page()
> >         arm_v7s_do_selftests()
> >
> > So, the results can be further filtered if you want a specified arch.
>=20
> So what is it just for x86? Could you tell?

I can probably figure out how to do additional filtering here, but does
it really matter for the case that is being discussed here? Andi's point wa=
s
that there quite many existing places in the kernel when low-level IO
happens before the probe stage. So I brought these numbers here.
What do you plan to do with the pure x86 results?=20

And here are the full results for allyesconfig, if anyone is interested (ju=
st got permission to create
the repository today):
https://github.com/intel/ccc-linux-guest-hardening/tree/master/audit/sample=
_output/5.15-rc1
We will be pushing to this repo all the scripts and fuzzing setups we use a=
s part of
our Linux guest hardening effort for confidential cloud computing, but it i=
s going to take
some time to get all the approvals collected. =20

Best Regards,
Elena.