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x86: SHADOW_PAGING is deprecated
Addressing certain issues, in particular related to operations which may
take excessively long and therefore would need preemption, has turned out
overly costly. Since alternatives (HVM/PVH: HAP, PV: shim) are commonly
available, the decision was to deprecate the functionality, while still
retaining it for people to use at their own (security) risk. Memory-wise
small enough guests may still be okay to run.
Some CI testing depends on SHADOW_PAGING. Explicitly enable it when needed.
This is CVE-2026-42493 / XSA-495.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
(cherry picked from commit f2cac32029)
This commit is contained in:
Jan Beulich authored and Andrew Cooper committed
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@@ -351,6 +351,16 @@ This is typically done by a guest kernel agent known as a "balloon driver".
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Status: Supported
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Status: Supported
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### Shadow paging
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Allows fully virtualized guests (HVM / PVH) to be run without (host side) page
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translation support by hardware (AMD: NPT, Intel: EPT).
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It is also required to migrate PV guests, and to allow L1TF-vulnerable guests
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to continue to run without compromising host security.
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Status: Supported, not security supported
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### Populate-on-demand memory
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### Populate-on-demand memory
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This is a mechanism that allows normal operating systems with only a balloon driver
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This is a mechanism that allows normal operating systems with only a balloon driver
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@@ -476,7 +486,7 @@ This feature is independent
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of the ARM "page granularity" feature (see below).
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of the ARM "page granularity" feature (see below).
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Status, x86 HVM/PVH, HAP: Supported
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Status, x86 HVM/PVH, HAP: Supported
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Status, x86 HVM/PVH, Shadow, 2MiB: Supported
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Status, x86 HVM/PVH, Shadow, 2MiB: Supported, not security supported
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Status, ARM: Supported
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Status, ARM: Supported
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On x86 in shadow mode, only 2MiB (L2) superpages are available;
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On x86 in shadow mode, only 2MiB (L2) superpages are available;
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@@ -307,11 +307,15 @@ debian-12-x86_64-gcc-debug:
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extends: .gcc-x86-64-build-debug
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extends: .gcc-x86-64-build-debug
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variables:
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variables:
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CONTAINER: debian:12-x86_64
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CONTAINER: debian:12-x86_64
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EXTRA_XEN_CONFIG: |
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CONFIG_SHADOW_PAGING=y
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debian-12-x86_64-clang-debug:
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debian-12-x86_64-clang-debug:
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extends: .clang-x86-64-build-debug
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extends: .clang-x86-64-build-debug
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variables:
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variables:
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CONTAINER: debian:12-x86_64
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CONTAINER: debian:12-x86_64
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EXTRA_XEN_CONFIG: |
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CONFIG_SHADOW_PAGING=y
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debian-12-ppc64le-gcc-debug:
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debian-12-ppc64le-gcc-debug:
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extends: .gcc-ppc64le-cross-build-debug
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extends: .gcc-ppc64le-cross-build-debug
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@@ -155,7 +155,6 @@ config XEN_IBT
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config SHADOW_PAGING
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config SHADOW_PAGING
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bool "Shadow Paging"
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bool "Shadow Paging"
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default !PV_SHIM_EXCLUSIVE
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depends on PV || HVM
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depends on PV || HVM
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help
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help
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@@ -171,7 +170,8 @@ config SHADOW_PAGING
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Under a small number of specific workloads, shadow paging may be
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Under a small number of specific workloads, shadow paging may be
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deliberately used as a performance optimisation.
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deliberately used as a performance optimisation.
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If unsure, say Y.
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NOTE: This feature is now deprecated. It is in particular no longer
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security supported.
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config BIGMEM
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config BIGMEM
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bool "big memory support"
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bool "big memory support"
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