On 3/3/22 16:41, David Woodhouse wrote:
This series adds event channel acceleration for Xen guests. In particular
it allows guest vCPUs to send each other IPIs without having to bounce
all the way out to the userspace VMM in order to do so. Likewise, the
Xen singleshot timer is added, and a version of SCHEDOP_poll. Those
major features are based on Joao and Boris' patches from 2019.
Cleaning up the event delivery into the vcpu_info involved using the new
gfn_to_pfn_cache for that, and that means I ended up doing so for *all*
the places the guest can have a pvclock.
v0: Proof-of-concept RFC
v1:
• Drop the runstate fix which is merged now.
• Add Sean's gfn_to_pfn_cache API change at the start of the series.
• Add KVM self tests
• Minor bug fixes
v2:
• Drop dirty handling from gfn_to_pfn_cache
• Fix !CONFIG_KVM_XEN build and duplicate call to kvm_xen_init_vcpu()
v3:
• Add KVM_XEN_EVTCHN_RESET to clear all outbound ports.
• Clean up a stray #if 1 in a part of the the test case that was once
being recalcitrant.
• Check kvm_xen_has_pending_events() in kvm_vcpu_has_events() and *not*
kvm_xen_has_pending_timer() which is checked from elsewhere.
• Fix warnings noted by the kernel test robot <lkp@xxxxxxxxx>:
• Make kvm_xen_init_timer() static.
• Make timer delta calculation use an explicit s64 to fix 32-bit build.
I've seen this:
[1790637.031490] BUG: Bad page state in process qemu-kvm pfn:03401
[1790637.037503] page:0000000077fc41af refcount:0 mapcount:1
mapping:0000000000000000 index:0x7f4ab7e01 pfn:0x3401
[1790637.047592] head:0000000032101bf5 order:9 compound_mapcount:1
compound_pincount:0
[1790637.055250] anon flags:
0xfffffc009000e(referenced|uptodate|dirty|head|swapbacked|node=0|zone=1|lastcpupid=0x1fffff)
[1790637.065949] raw: 000fffffc0000000 ffffda4b800d0001 0000000000000903
dead000000000200
[1790637.073869] raw: 0000000000000100 0000000000000000 00000000ffffffff
0000000000000000
[1790637.081791] head: 000fffffc009000e dead000000000100
dead000000000122 ffffa0636279fb01
[1790637.089797] head: 00000007f4ab7e00 0000000000000000
00000000ffffffff 0000000000000000
[1790637.097795] page dumped because: nonzero compound_mapcount
[1790637.103455] Modules linked in: kvm_intel(OE) kvm(OE) overlay tun
tls ib_core rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd
grace fscache netfs rfkill sunrpc intel_rapl_msr intel_rapl_common
isst_if_common skx_edac nfit libnvdimm x86_pkg_temp_thermal
intel_powerclamp coretemp ipmi_ssif iTCO_wdt intel_pmc_bxt irqbypass
iTCO_vendor_support acpi_ipmi rapl dell_smbios ipmi_si mei_me
intel_cstate dcdbas ipmi_devintf i2c_i801 intel_uncore
dell_wmi_descriptor wmi_bmof mei lpc_ich intel_pch_thermal i2c_smbus
ipmi_msghandler acpi_power_meter xfs crct10dif_pclmul i40e crc32_pclmul
crc32c_intel megaraid_sas ghash_clmulni_intel tg3 mgag200 wmi fuse [last
unloaded: kvm]
[1790637.162636] CPU: 12 PID: 3056318 Comm: qemu-kvm Kdump: loaded
Tainted: G W IOE --------- --- 5.16.0-0.rc6.41.fc36.x86_64 #1
[1790637.174878] Hardware name: Dell Inc. PowerEdge R440/08CYF7, BIOS
1.6.11 11/20/2018
[1790637.182618] Call Trace:
[1790637.185246] <TASK>
[1790637.187524] dump_stack_lvl+0x48/0x5e
[1790637.191373] bad_page.cold+0x63/0x94
[1790637.195123] free_tail_pages_check+0xbb/0x110
[1790637.199656] free_pcp_prepare+0x270/0x310
[1790637.203843] free_unref_page+0x1d/0x120
[1790637.207856] kvm_gfn_to_pfn_cache_refresh+0x2c2/0x400 [kvm]
[1790637.213662] kvm_setup_guest_pvclock+0x4b/0x180 [kvm]
[1790637.218913] kvm_guest_time_update+0x26d/0x330 [kvm]
[1790637.224080] vcpu_enter_guest+0x31c/0x1390 [kvm]
[1790637.228908] kvm_arch_vcpu_ioctl_run+0x132/0x830 [kvm]
[1790637.234254] kvm_vcpu_ioctl+0x270/0x680 [kvm]
followed by other badness with the same call stack:
[1790637.376127] page dumped because:
VM_BUG_ON_PAGE(page_ref_count(page) == 0)
I am absolutely not sure that this series is the culprit in any way, but
anyway I'll try to reproduce (it happened at the end of a RHEL7.2
installation) and let you know. If not, it is something that already
made its way to Linus.
Paolo
