5.15-stable patches

added patches:
	revert-kvm-x86-enable-tdp-mmu-by-default.patch

diff --git a/queue-5.15/revert-kvm-x86-enable-tdp-mmu-by-default.patch b/queue-5.15/revert-kvm-x86-enable-tdp-mmu-by-default.patch
new file mode 100644 (file)
index 0000000..b8929be
--- /dev/null
+++ b/queue-5.15/revert-kvm-x86-enable-tdp-mmu-by-default.patch
@@ -0,0 +1,80 @@
+From seanjc@google.com  Sat Aug 26 18:36:13 2023
+From: Sean Christopherson <seanjc@google.com>
+Date: Wed, 23 Aug 2023 18:05:12 -0700
+Subject: Revert "KVM: x86: enable TDP MMU by default"
+To: stable@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Cc: Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org
+Message-ID: <20230824010512.2714931-1-seanjc@google.com>
+
+From: Sean Christopherson <seanjc@google.com>
+
+This reverts commit 71ba3f3189c78f756a659568fb473600fd78f207.
+
+Disable the TDP MMU by default in v5.15 kernels to "fix" several severe
+performance bugs that have since been found and fixed in the TDP MMU, but
+are unsuitable for backporting to v5.15.
+
+The problematic bugs are fixed by upstream commit edbdb43fc96b ("KVM:
+x86: Preserve TDP MMU roots until they are explicitly invalidated") and
+commit 01b31714bd90 ("KVM: x86: Do not unload MMU roots when only toggling
+CR0.WP with TDP enabled").  Both commits fix scenarios where KVM will
+rebuild all TDP MMU page tables in paths that are frequently hit by
+certain guest workloads.  While not exactly common, the guest workloads
+are far from rare.  The fallout of rebuilding TDP MMU page tables can be
+so severe in some cases that it induces soft lockups in the guest.
+
+Commit edbdb43fc96b would require _significant_ effort and churn to
+backport due it depending on a major rework that was done in v5.18.
+
+Commit 01b31714bd90 has far fewer direct conflicts, but has several subtle
+_known_ dependencies, and it's unclear whether or not there are more
+unknown dependencies that have been missed.
+
+Lastly, disabling the TDP MMU in v5.15 kernels also fixes a lurking train
+wreck started by upstream commit a955cad84cda ("KVM: x86/mmu: Retry page
+fault if root is invalidated by memslot update").  That commit was tagged
+for stable to fix a memory leak, but didn't cherry-pick cleanly and was
+never backported to v5.15.  Which is extremely fortunate, as it introduced
+not one but two bugs, one of which was fixed by upstream commit
+18c841e1f411 ("KVM: x86: Retry page fault if MMU reload is pending and
+root has no sp"), while the other was unknowingly fixed by upstream
+commit ba6e3fe25543 ("KVM: x86/mmu: Grab mmu_invalidate_seq in
+kvm_faultin_pfn()") in v6.3 (a one-off fix will be made for v6.1 kernels,
+which did receive a backport for a955cad84cda).  Disabling the TDP MMU
+by default reduces the probability of breaking v5.15 kernels by
+backporting only a subset of the fixes.
+
+As far as what is lost by disabling the TDP MMU, the main selling point of
+the TDP MMU is its ability to service page fault VM-Exits in parallel,
+i.e. the main benefactors of the TDP MMU are deployments of large VMs
+(hundreds of vCPUs), and in particular delployments that live-migrate such
+VMs and thus need to fault-in huge amounts of memory on many vCPUs after
+restarting the VM after migration.
+
+Smaller VMs can see performance improvements, but nowhere enough to make
+up for the TDP MMU (in v5.15) absolutely cratering performance for some
+workloads.  And practically speaking, anyone that is deploying and
+migrating VMs with hundreds of vCPUs is likely rolling their own kernel,
+not using a stock v5.15 series kernel.
+
+Link: https://lore.kernel.org/all/ZDmEGM+CgYpvDLh6@google.com
+Link: https://lore.kernel.org/all/f023d927-52aa-7e08-2ee5-59a2fbc65953@gameservers.com
+Acked-by: Mathias Krause <minipli@grsecurity.net>
+Acked-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
+Signed-off-by: Sean Christopherson <seanjc@google.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/kvm/mmu/tdp_mmu.c |    2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/arch/x86/kvm/mmu/tdp_mmu.c
++++ b/arch/x86/kvm/mmu/tdp_mmu.c
+@@ -10,7 +10,7 @@
+ #include <asm/cmpxchg.h>
+ #include <trace/events/kvm.h>
+ 
+-static bool __read_mostly tdp_mmu_enabled = true;
++static bool __read_mostly tdp_mmu_enabled = false;
+ module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0644);
+ 
+ /* Initializes the TDP MMU for the VM, if enabled. */

diff --git a/queue-5.15/series b/queue-5.15/series
index b6873f7ce9859b2dfdc8b5403845411ce32a72aa..c4ca0c017acec8ce8b334fe659a843b35b46cc4f 100644 (file)
--- a/queue-5.15/series
+++ b/queue-5.15/series
@@ -45,3 +45,4 @@ net-remove-bond_slave_has_mac_rcu.patch
 bonding-fix-macvlan-over-alb-bond-support.patch
 net-ncsi-make-one-oem_gma-function-for-all-mfr-id.patch
 net-ncsi-change-from-ndo_set_mac_address-to-dev_set_mac_address.patch
+revert-kvm-x86-enable-tdp-mmu-by-default.patch