Xiaoyao Li ccb2280ec2 x86/kvm: Use separate percpu variable to track the enabling of asyncpf ... Refer to commit fd10cde929 ("KVM paravirt: Add async PF initialization to PV guest") and commit 344d9588a9 ("KVM: Add PV MSR to enable asynchronous page faults delivery"). It turns out that at the time when asyncpf was introduced, the purpose was defining the shared PV data 'struct kvm_vcpu_pv_apf_data' with the size of 64 bytes. However, it made a mistake and defined the size to 68 bytes, which failed to make fit in a cache line and made the code inconsistent with the documentation. Below justification quoted from Sean[*] KVM (the host side) has *never* read kvm_vcpu_pv_apf_data.enabled, and the documentation clearly states that enabling is based solely on the bit in the synthetic MSR. So rather than update the documentation, fix the goof by removing the enabled filed and use the separate percpu variable instread. KVM-as-a-host obviously doesn't enforce anything or consume the size, and changing the header will only affect guests that are rebuilt against the new header, so there's no chance of ABI breakage between KVM and its guests. The only possible breakage is if some other hypervisor is emulating KVM's async #PF (LOL) and relies on the guest to set kvm_vcpu_pv_apf_data.enabled. But (a) I highly doubt such a hypervisor exists, (b) that would arguably be a violation of KVM's "spec", and (c) the worst case scenario is that the guest would simply lose async #PF functionality. [*] https://lore.kernel.org/all/ZS7ERnnRqs8Fl0ZF@google.com/T/#u Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com> Link: https://lore.kernel.org/r/20231025055914.1201792-2-xiaoyao.li@intel.com [sean: use true/false instead of 1/0 for booleans] Signed-off-by: Sean Christopherson <seanjc@google.com>		2024-02-06 10:58:56 -08:00
..
arm	KVM: arm64: Document vCPU feature selection UAPIs	2023-10-04 17:11:51 +00:00
devices	KVM: arm64: Clarify the ordering requirements for vcpu/RD creation	2023-09-30 18:15:44 +00:00
s390	ARM:	2022-08-04 14:59:54 -07:00
x86	x86/kvm: Use separate percpu variable to track the enabling of asyncpf	2024-02-06 10:58:56 -08:00
api.rst	KVM Xen change for 6.8:	2024-01-08 08:10:20 -05:00
halt-polling.rst	Documentation: Fix typos	2023-08-18 11:29:03 -06:00
index.rst	KVM: Move halt-polling documentation into common directory	2022-12-02 13:20:30 -05:00
locking.rst	KVM: x86/mmu: always take tdp_mmu_pages_lock	2023-12-01 07:52:08 -08:00
ppc-pv.rst	Documentation: KVM: make corrections to ppc-pv.rst	2023-06-16 08:20:53 -06:00
review-checklist.rst	docs: fix broken references for ReST files that moved around	2020-04-20 15:45:03 -06:00
vcpu-requests.rst	Documentation: KVM: make corrections to vcpu-requests.rst	2023-06-16 08:20:53 -06:00