- 01 Oct, 2021 38 commits
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Babu Moger authored
Predictive Store Forwarding: AMD Zen3 processors feature a new technology called Predictive Store Forwarding (PSF). PSF is a hardware-based micro-architectural optimization designed to improve the performance of code execution by predicting address dependencies between loads and stores. How PSF works: It is very common for a CPU to execute a load instruction to an address that was recently written by a store. Modern CPUs implement a technique known as Store-To-Load-Forwarding (STLF) to improve performance in such cases. With STLF, data from the store is forwarded directly to the load without having to wait for it to be written to memory. In a typical CPU, STLF occurs after the address of both the load and store are calculated and determined to match. PSF expands on this by speculating on the relationship between loads and stores without waiting for the address calculation to complete. With PSF, the CPU learns over time the relationship between loads and stores. If STLF typically occurs between a particular store and load, the CPU will remember this. In typical code, PSF provides a performance benefit by speculating on the load result and allowing later instructions to begin execution sooner than they otherwise would be able to. The details of security analysis of AMD predictive store forwarding is documented here. https://www.amd.com/system/files/documents/security-analysis-predictive-store-forwarding.pdf Predictive Store Forwarding controls: There are two hardware control bits which influence the PSF feature: - MSR 48h bit 2 – Speculative Store Bypass (SSBD) - MSR 48h bit 7 – Predictive Store Forwarding Disable (PSFD) The PSF feature is disabled if either of these bits are set. These bits are controllable on a per-thread basis in an SMT system. By default, both SSBD and PSFD are 0 meaning that the speculation features are enabled. While the SSBD bit disables PSF and speculative store bypass, PSFD only disables PSF. PSFD may be desirable for software which is concerned with the speculative behavior of PSF but desires a smaller performance impact than setting SSBD. Support for PSFD is indicated in CPUID Fn8000_0008 EBX[28]. All processors that support PSF will also support PSFD. Linux kernel does not have the interface to enable/disable PSFD yet. Plan here is to expose the PSFD technology to KVM so that the guest kernel can make use of it if they wish to. Signed-off-by:
Babu Moger <Babu.Moger@amd.com> Message-Id: <163244601049.30292.5855870305350227855.stgit@bmoger-ubuntu> [Keep feature private to KVM, as requested by Borislav Petkov. - Paolo] Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com>
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David Matlack authored
mmu_try_to_unsync_pages checks if page tracking is active for the given gfn, which requires knowing the memslot. We can pass down the memslot via make_spte to avoid this lookup. The memslot is also handy for make_spte's marking of the gfn as dirty: we can test whether dirty page tracking is enabled, and if so ensure that pages are mapped as writable with 4K granularity. Apart from the warning, no functional change is intended. Signed-off-by:
David Matlack <dmatlack@google.com> Message-Id: <20210813203504.2742757-7-dmatlack@google.com> Signed-off-by:
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David Matlack authored
Avoid the memslot lookup in rmap_add, by passing it down from the fault handling code to mmu_set_spte and then to rmap_add. No functional change intended. Signed-off-by:
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Paolo Bonzini authored
mmu_set_spte is called for either PTE prefetching or page faults. The three boolean arguments write_fault, speculative and host_writable are always respectively false/true/true for prefetching and coming from a struct kvm_page_fault for page faults. Let mmu_set_spte distinguish these two situation by accepting a possibly NULL struct kvm_page_fault argument. Signed-off-by: -
Paolo Bonzini authored
The level and A/D bit support of the new SPTE can be found in the role, which is stored in the kvm_mmu_page struct. This merges two arguments into one. For the TDP MMU, the kvm_mmu_page was not used (kvm_tdp_mmu_map does not use it if the SPTE is already present) so we fetch it just before calling make_spte. Signed-off-by: -
Paolo Bonzini authored
Prepare for removing the ad_disabled argument of make_spte; instead it can be found in the role of a struct kvm_mmu_page. First of all, the TDP MMU must set the role accurately. Signed-off-by: -
Paolo Bonzini authored
The level of the new SPTE can be found in the kvm_mmu_page struct; there is no need to pass it down. Signed-off-by: -
Paolo Bonzini authored
Now that make_spte is called directly by the shadow MMU (rather than wrapped by set_spte), it only has to return one boolean value. Signed-off-by: -
Paolo Bonzini authored
Since the two callers of set_spte do different things with the results, inlining it actually makes the code simpler to reason about. For example, FNAME(sync_page) already has a struct kvm_mmu_page *, but set_spte had to fish it back out of sptep's private page data. Signed-off-by: -
Paolo Bonzini authored
Since the two callers of set_spte do different things with the results, inlining it actually makes the code simpler to reason about. For example, mmu_set_spte looks quite like tdp_mmu_map_handle_target_level, but the similarity is hidden by set_spte. Signed-off-by: -
David Matlack authored
Now that kvm_page_fault has a pointer to the memslot it can be passed down to the page tracking code to avoid a redundant slot lookup. No functional change intended. Signed-off-by:
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David Matlack authored
The memslot for the faulting gfn is used throughout the page fault handling code, so capture it in kvm_page_fault as soon as we know the gfn and use it in the page fault handling code that has direct access to the kvm_page_fault struct. Replace various tests using is_noslot_pfn with more direct tests on fault->slot being NULL. This, in combination with the subsequent patch, improves "Populate memory time" in dirty_log_perf_test by 5% when using the legacy MMU. There is no discerable improvement to the performance of the TDP MMU. No functional change intended. Suggested-by:
Ben Gardon <bgardon@google.com> Signed-off-by:
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Paolo Bonzini authored
tdp_mmu_map_set_spte_atomic is not taking care of dirty logging anymore, the only difference that remains is that it takes a vCPU instead of the struct kvm. Merge the two functions. Signed-off-by: -
Paolo Bonzini authored
This simplifies set_spte, which we want to remove, and unifies code between the shadow MMU and the TDP MMU. The warning will be added back later to make_spte as well. There is a small disadvantage in the TDP MMU; it may unnecessarily mark a page as dirty twice if two vCPUs end up mapping the same page twice. However, this is a very small cost for a case that is already rare. Signed-off-by: -
David Matlack authored
Consolidate rmap_recycle and rmap_add into a single function since they are only ever called together (and only from one place). This has a nice side effect of eliminating an extra kvm_vcpu_gfn_to_memslot(). In addition it makes mmu_set_spte(), which is a very long function, a little shorter. No functional change intended. Signed-off-by:
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Sean Christopherson authored
WARN and bail if the shadow walk for faulting in a SPTE terminates early, i.e. doesn't reach the expected level because the walk encountered a terminal SPTE. The shadow walks for page faults are subtle in that they install non-leaf SPTEs (zapping leaf SPTEs if necessary!) in the loop body, and consume the newly created non-leaf SPTE in the loop control, e.g. __shadow_walk_next(). In other words, the walks guarantee that the walk will stop if and only if the target level is reached by installing non-leaf SPTEs to guarantee the walk remains valid. Opportunistically use fault->goal-level instead of it.level in FNAME(fetch) to further clarify that KVM always installs the leaf SPTE at the target level. Reviewed-by:
Lai Jiangshan <jiangshanlai@gmail.com> Signed-off-by:
Sean Christopherson <seanjc@google.com> Signed-off-by:
Lai Jiangshan <laijs@linux.alibaba.com> Message-Id: <20210906122547.263316-1-jiangshanlai@gmail.com> Signed-off-by:
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Paolo Bonzini authored
Pass struct kvm_page_fault to tracepoints instead of extracting the arguments from the struct. This also lets the kvm_mmu_spte_requested tracepoint pick the gfn directly from fault->gfn, instead of using the address. Signed-off-by: -
Paolo Bonzini authored
Pass struct kvm_page_fault to disallowed_hugepage_adjust() instead of extracting the arguments from the struct. Tweak a bit the conditions to avoid long lines. Signed-off-by: -
Paolo Bonzini authored
Pass struct kvm_page_fault to kvm_mmu_hugepage_adjust() instead of extracting the arguments from the struct; the results are also stored in the struct, so the callers are adjusted consequently. Signed-off-by: -
Paolo Bonzini authored
Pass struct kvm_page_fault to fast_page_fault() instead of extracting the arguments from the struct. Suggested-by:
Isaku Yamahata <isaku.yamahata@intel.com> Signed-off-by:
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Paolo Bonzini authored
Pass struct kvm_page_fault to tdp_mmu_map_handle_target_level() instead of extracting the arguments from the struct. Signed-off-by: -
Paolo Bonzini authored
Pass struct kvm_page_fault to kvm_tdp_mmu_map() instead of extracting the arguments from the struct. Suggested-by:
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Paolo Bonzini authored
Pass struct kvm_page_fault to FNAME(fetch)() instead of extracting the arguments from the struct. Suggested-by:
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Paolo Bonzini authored
Pass struct kvm_page_fault to __direct_map() instead of extracting the arguments from the struct. Suggested-by:
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Paolo Bonzini authored
Pass struct kvm_page_fault to handle_abnormal_pfn() instead of extracting the arguments from the struct. Suggested-by:
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Paolo Bonzini authored
Add fields to struct kvm_page_fault corresponding to outputs of kvm_faultin_pfn(). For now they have to be extracted again from struct kvm_page_fault in the subsequent steps, but this is temporary until other functions in the chain are switched over as well. Suggested-by:
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Paolo Bonzini authored
Add fields to struct kvm_page_fault corresponding to the arguments of page_fault_handle_page_track(). The fields are initialized in the callers, and page_fault_handle_page_track() receives a struct kvm_page_fault instead of having to extract the arguments out of it. Suggested-by:
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Paolo Bonzini authored
Add fields to struct kvm_page_fault corresponding to the arguments of direct_page_fault(). The fields are initialized in the callers, and direct_page_fault() receives a struct kvm_page_fault instead of having to extract the arguments out of it. Also adjust FNAME(page_fault) to store the max_level in struct kvm_page_fault, to keep it similar to the direct map path. Suggested-by:
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Paolo Bonzini authored
Pass struct kvm_page_fault to mmu->page_fault() instead of extracting the arguments from the struct. FNAME(page_fault) can use the precomputed bools from the error code. Suggested-by:
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Paolo Bonzini authored
Create a single structure for arguments that are passed from kvm_mmu_do_page_fault to the page fault handlers. Later the structure will grow to include various output parameters that are passed back to the next steps in the page fault handling. Suggested-by:
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Paolo Bonzini authored
Do not bother removing the low bits of the gpa. This masking dates back to the very first commit of KVM but it is unnecessary, as exemplified by the other call in kvm_tdp_page_fault. Signed-off-by: -
Oliver Upton authored
Sean noticed that KVM_GET_CLOCK was checking kvm_arch.use_master_clock outside of the pvclock sync lock. This is problematic, as the clock value written to the user may or may not actually correspond to a stable TSC. Fix the race by populating the entire kvm_clock_data structure behind the pvclock_gtod_sync_lock. Suggested-by:
Oliver Upton <oupton@google.com> Message-Id: <20210916181538.968978-4-oupton@google.com> Reviewed-by:
Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by:
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Paolo Bonzini authored
No functional change intended. Reviewed-by:
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Paolo Bonzini authored
Updates to the kvmclock parameters needs to do a complicated dance of KVM_REQ_MCLOCK_INPROGRESS and KVM_REQ_CLOCK_UPDATE in addition to taking pvclock_gtod_sync_lock. Place that in two functions that can be called on all of master clock update, KVM_SET_CLOCK, and Hyper-V reenlightenment. Reviewed-by:
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Lai Jiangshan authored
So far, the loop bodies already ensure the PTE is present before calling __shadow_walk_next(): Some loop bodies simply exit with a !PRESENT directly and some other loop bodies, i.e. FNAME(fetch) and __direct_map() do not currently guard their walks with is_shadow_present_pte, but only because they install present non-leaf SPTEs in the loop itself. But checking pte present in __shadow_walk_next() (which is called from shadow_walk_okay()) is more prudent; walking past a !PRESENT SPTE would lead to attempting to read a the next level SPTE from a garbage iter->shadow_addr. It also allows to remove the is_shadow_present_pte() checks from the loop bodies. Reviewed-by:
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Maxim Levitsky authored
This was tested by booting a nested guest with TSC=1Ghz, observing the clocks, and doing about 100 cycles of migration. Note that qemu patch is needed to support migration because of a new MSR that needs to be placed in the migration state. The patch will be sent to the qemu mailing list soon. Signed-off-by:
Maxim Levitsky <mlevitsk@redhat.com> Message-Id: <20210914154825.104886-14-mlevitsk@redhat.com> Signed-off-by:
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Maxim Levitsky authored
This allows to easily simulate a CPU without this feature. Signed-off-by:
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Paolo Bonzini authored
Commit adc2a237 ("KVM: nSVM: improve SYSENTER emulation on AMD"), made init_vmcb set vmload/vmsave intercepts unconditionally, and relied on svm_vcpu_after_set_cpuid to clear them when possible. However init_vmcb is also called when the vCPU is reset, and it is not followed by another call to svm_vcpu_after_set_cpuid because the CPUID is already set. This mistake makes the VMSAVE/VMLOAD intercept to be set when it is not needed, and harms performance of the nested guest. Extract the relevant parts of svm_vcpu_after_set_cpuid so that they can be called again on reset. Fixes: adc2a237 ("KVM: nSVM: improve SYSENTER emulation on AMD") Signed-off-by:
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- 30 Sep, 2021 2 commits
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Maxim Levitsky authored
This is useful for debug and also makes it consistent with the rest of the SVM optional features. Signed-off-by:
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Maxim Levitsky authored
According to the SDM, the CPU never modifies these settings. It loads them on VM entry and updates an internal copy instead. Also don't load them from the vmcb12 as we don't expose these features to the nested guest yet. Signed-off-by:
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