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Filename Latest commit message Latest commit date
Nadav Amit e857e21eb2 iommu/vt-d: Do not use flush-queue when caching-mode is on 
commit 29b32839725f8c89a41cb6ee054c85f3116ea8b5 upstream.

When an Intel IOMMU is virtualized, and a physical device is
passed-through to the VM, changes of the virtual IOMMU need to be
propagated to the physical IOMMU. The hypervisor therefore needs to
monitor PTE mappings in the IOMMU page-tables. Intel specifications
provide "caching-mode" capability that a virtual IOMMU uses to report
that the IOMMU is virtualized and a TLB flush is needed after mapping to
allow the hypervisor to propagate virtual IOMMU mappings to the physical
IOMMU. To the best of my knowledge no real physical IOMMU reports
"caching-mode" as turned on.

Synchronizing the virtual and the physical IOMMU tables is expensive if
the hypervisor is unaware which PTEs have changed, as the hypervisor is
required to walk all the virtualized tables and look for changes.
Consequently, domain flushes are much more expensive than page-specific
flushes on virtualized IOMMUs with passthrough devices. The kernel
therefore exploited the "caching-mode" indication to avoid domain
flushing and use page-specific flushing in virtualized environments. See
commit 78d5f0f500 ("intel-iommu: Avoid global flushes with caching
mode.")

This behavior changed after commit 13cf017446 ("iommu/vt-d: Make use
of iova deferred flushing"). Now, when batched TLB flushing is used (the
default), full TLB domain flushes are performed frequently, requiring
the hypervisor to perform expensive synchronization between the virtual
TLB and the physical one.

Getting batched TLB flushes to use page-specific invalidations again in
such circumstances is not easy, since the TLB invalidation scheme
assumes that "full" domain TLB flushes are performed for scalability.

Disable batched TLB flushes when caching-mode is on, as the performance
benefit from using batched TLB invalidations is likely to be much
smaller than the overhead of the virtual-to-physical IOMMU page-tables
synchronization.

Fixes: 13cf017446 ("iommu/vt-d: Make use of iova deferred flushing")
Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Will Deacon <will@kernel.org>
Cc: stable@vger.kernel.org
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210127175317.1600473-1-namit@vmware.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-02-10 09:25:32 +01:00
arch x86/apic: Add extra serialization for non-serializing MSRs 2021-02-10 09:25:32 +01:00
block Revert "Revert "block: end bio with BLK_STS_AGAIN in case of non-mq devs and REQ_NOWAIT"" 2021-02-07 15:35:47 +01:00
certs
crypto crypto: asym_tpm: correct zero out potential secrets 2021-01-12 20:16:17 +01:00
Documentation KVM: Forbid the use of tagged userspace addresses for memslots 2021-02-03 23:25:57 +01:00
drivers iommu/vt-d: Do not use flush-queue when caching-mode is on 2021-02-10 09:25:32 +01:00
fs mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page 2021-02-10 09:25:31 +01:00
include mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page 2021-02-10 09:25:31 +01:00
init fgraph: Initialize tracing_graph_pause at task creation 2021-02-10 09:25:29 +01:00
ipc
kernel genirq/msi: Activate Multi-MSI early when MSI_FLAG_ACTIVATE_EARLY is set 2021-02-10 09:25:30 +01:00
lib lib/raid6: Let $(UNROLL) rules work with macOS userland 2021-01-19 18:26:15 +01:00
LICENSES
mm mm: thp: fix MADV_REMOVE deadlock on shmem THP 2021-02-10 09:25:31 +01:00
net mac80211: fix station rate table updates on assoc 2021-02-10 09:25:29 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-12 20:16:10 +01:00
security dump_common_audit_data(): fix racy accesses to ->d_name 2021-01-19 18:26:16 +01:00
sound ALSA: hda: Add Cometlake-R PCI ID 2021-02-07 15:35:49 +01:00
tools objtool: Don't fail on missing symbol table 2021-02-07 15:35:49 +01:00
usr
virt KVM: Forbid the use of tagged userspace addresses for memslots 2021-02-03 23:25:57 +01:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile x86/build: Disable CET instrumentation in the kernel 2021-02-10 09:25:32 +01:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.