KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/Documentation/arch/riscv/patch-acceptance.rst b/Documentation/arch/riscv/patch-acceptance.rst
new file mode 100644
index 000000000..634aa222b
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+++ b/Documentation/arch/riscv/patch-acceptance.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+arch/riscv maintenance guidelines for developers
+================================================
+
+Overview
+--------
+The RISC-V instruction set architecture is developed in the open:
+in-progress drafts are available for all to review and to experiment
+with implementations.  New module or extension drafts can change
+during the development process - sometimes in ways that are
+incompatible with previous drafts.  This flexibility can present a
+challenge for RISC-V Linux maintenance.  Linux maintainers disapprove
+of churn, and the Linux development process prefers well-reviewed and
+tested code over experimental code.  We wish to extend these same
+principles to the RISC-V-related code that will be accepted for
+inclusion in the kernel.
+
+Patchwork
+---------
+
+RISC-V has a patchwork instance, where the status of patches can be checked:
+
+  https://patchwork.kernel.org/project/linux-riscv/list/
+
+If your patch does not appear in the default view, the RISC-V maintainers have
+likely either requested changes, or expect it to be applied to another tree.
+
+Automation runs against this patchwork instance, building/testing patches as
+they arrive. The automation applies patches against the current HEAD of the
+RISC-V `for-next` and `fixes` branches, depending on whether the patch has been
+detected as a fix. Failing those, it will use the RISC-V `master` branch.
+The exact commit to which a series has been applied will be noted on patchwork.
+Patches for which any of the checks fail are unlikely to be applied and in most
+cases will need to be resubmitted.
+
+Submit Checklist Addendum
+-------------------------
+We'll only accept patches for new modules or extensions if the
+specifications for those modules or extensions are listed as being
+unlikely to be incompatibly changed in the future.  For
+specifications from the RISC-V foundation this means "Frozen" or
+"Ratified", for the UEFI forum specifications this means a published
+ECR.  (Developers may, of course, maintain their own Linux kernel trees
+that contain code for any draft extensions that they wish.)
+
+Additionally, the RISC-V specification allows implementers to create
+their own custom extensions.  These custom extensions aren't required
+to go through any review or ratification process by the RISC-V
+Foundation.  To avoid the maintenance complexity and potential
+performance impact of adding kernel code for implementor-specific
+RISC-V extensions, we'll only consider patches for extensions that either:
+
+- Have been officially frozen or ratified by the RISC-V Foundation, or
+- Have been implemented in hardware that is widely available, per standard
+  Linux practice.
+
+(Implementers, may, of course, maintain their own Linux kernel trees containing
+code for any custom extensions that they wish.)