Ben Gardon 7cca2d0b7e KVM: x86/mmu: Protect TDP MMU page table memory with RCU ... In order to enable concurrent modifications to the paging structures in the TDP MMU, threads must be able to safely remove pages of page table memory while other threads are traversing the same memory. To ensure threads do not access PT memory after it is freed, protect PT memory with RCU. Protecting concurrent accesses to page table memory from use-after-free bugs could also have been acomplished using walk_shadow_page_lockless_begin/end() and READING_SHADOW_PAGE_TABLES, coupling with the barriers in a TLB flush. The use of RCU for this case has several distinct advantages over that approach. 1. Disabling interrupts for long running operations is not desirable. Future commits will allow operations besides page faults to operate without the exclusive protection of the MMU lock and those operations are too long to disable iterrupts for their duration. 2. The use of RCU here avoids long blocking / spinning operations in perfromance critical paths. By freeing memory with an asynchronous RCU API we avoid the longer wait times TLB flushes experience when overlapping with a thread in walk_shadow_page_lockless_begin/end(). 3. RCU provides a separation of concerns when removing memory from the paging structure. Because the RCU callback to free memory can be scheduled immediately after a TLB flush, there's no need for the thread to manually free a queue of pages later, as commit_zap_pages does. Fixes: 95fb5b0258 ("kvm: x86/mmu: Support MMIO in the TDP MMU") Reviewed-by: Peter Feiner <pfeiner@google.com> Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Ben Gardon <bgardon@google.com> Message-Id: <20210202185734.1680553-18-bgardon@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>		2021-02-04 05:27:42 -05:00
..
mmu_audit.c	KVM: Stop using deprecated jump label APIs	2021-02-04 05:27:29 -05:00
mmu_internal.h	KVM: x86/mmu: Protect TDP MMU page table memory with RCU	2021-02-04 05:27:42 -05:00
mmu.c	KVM: x86/mmu: Fix braces in kvm_recover_nx_lpages	2021-02-04 05:27:39 -05:00
mmutrace.h	kvm: x86/mmu: Add TDP MMU SPTE changed trace point	2020-11-19 10:57:16 -05:00
page_track.c	kvm: mmu: page_track: Fix RCU list API usage	2020-08-24 18:36:23 -07:00
paging_tmpl.h	kvm: x86/mmu: Remove disallowed_hugepage_adjust shadow_walk_iterator arg	2020-10-21 18:17:02 -04:00
spte.c	KVM: x86: use static calls to reduce kvm_x86_ops overhead	2021-02-04 05:27:30 -05:00
spte.h	KVM: x86/mmu: Use boolean returns for (S)PTE accessors	2021-02-04 05:27:15 -05:00
tdp_iter.c	KVM: x86/mmu: Protect TDP MMU page table memory with RCU	2021-02-04 05:27:42 -05:00
tdp_iter.h	KVM: x86/mmu: Protect TDP MMU page table memory with RCU	2021-02-04 05:27:42 -05:00
tdp_mmu.c	KVM: x86/mmu: Protect TDP MMU page table memory with RCU	2021-02-04 05:27:42 -05:00
tdp_mmu.h	KVM: x86/mmu: Get root level from walkers when retrieving MMIO SPTE	2021-01-07 18:00:24 -05:00