From: Greg Kroah-Hartman Date: Sat, 26 Aug 2023 16:48:05 +0000 (+0200) Subject: 5.15-stable patches X-Git-Tag: v6.1.49~64 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4626c6cbf57bdf3ec3d148f7e0c0e9e2288b7d23;p=thirdparty%2Fkernel%2Fstable-queue.git 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 index 00000000000..b8929be6705 --- /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 +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 +Cc: Paolo Bonzini , linux-kernel@vger.kernel.org +Message-ID: <20230824010512.2714931-1-seanjc@google.com> + +From: Sean Christopherson + +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 +Acked-by: Jeremi Piotrowski +Signed-off-by: Sean Christopherson +Signed-off-by: Greg Kroah-Hartman +--- + 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 + #include + +-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 b6873f7ce98..c4ca0c017ac 100644 --- 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