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
..
acrn	docs: acrn: Introduce ACRN	2021-02-09 10:58:18 +01:00
coco	x86/sev: Change snp_guest_issue_request()'s fw_err argument	2023-03-21 15:43:19 +01:00
hyperv	Documentation: Fix typos	2023-08-18 11:29:03 -06:00
kvm	x86/kvm: Use separate percpu variable to track the enabling of asyncpf	2024-02-06 10:58:56 -08:00
uml	Documentation: Fix typos	2023-08-18 11:29:03 -06:00
guest-halt-polling.rst	Documentation: virt: correct location of haltpoll module params	2023-06-16 08:17:21 -06:00
index.rst	Docs/subsystem-apis: Remove '[The ]Linux' prefixes from titles of listed documents	2023-01-24 15:27:08 -07:00
ne_overview.rst	nitro_enclaves: Update documentation for Arm64 support	2021-09-14 11:11:20 +02:00
paravirt_ops.rst	Documentation: virt: Clean up paravirt_ops doc	2023-06-19 12:09:54 +02:00