72 lines
3.1 KiB
Bash
Executable File
72 lines
3.1 KiB
Bash
Executable File
#!/bin/bash
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# Keeps the kvm_amd cpuid_passthrough switch correct across a guest's whole life,
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# in-guest reboots included.
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#
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# The switch must be OFF (N) while the guest enumerates CPUID at boot or Windows
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# hangs, and ON (Y) once it is up, where it clears the timer detection. The libvirt
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# hook only fires at VM start and stop, so a guest-initiated reboot would otherwise
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# re-enumerate with the switch still Y and hang. This watcher drops it to N on every
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# QEMU RESET and raises it again once the guest's NIC is back up.
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#
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# Readiness signal: the guest tap's rx_packets counter growing past a baseline. It
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# only moves once the guest NIC driver has loaded, well past CPU enumeration, and it
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# needs nothing enabled inside the guest. The counter is cumulative and does NOT
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# reset on an in-guest reboot, so readiness is growth past the value captured at the
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# reset, not an absolute threshold.
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#
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# Launched as a transient systemd unit by the cpuid-passthrough hook, so it is free
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# to call virsh (the hook itself must not - that deadlocks libvirtd).
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DOMAIN=$1
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BRAND=$2
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PARAM=/sys/module/kvm_amd/parameters
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V="virsh -c qemu:///system"
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running() { [ "$($V domstate "$DOMAIN" 2>/dev/null)" = running ]; }
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rx() { cat "$RX" 2>/dev/null || echo 0; }
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set_N() { echo N > "$PARAM/cpuid_passthrough"; }
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set_Y() { printf '%s' "$BRAND" > "$PARAM/brand_string"; echo Y > "$PARAM/cpuid_passthrough"; }
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# Wait until the tap rx counter grows at least 4 past $1 (guest NIC driver up again).
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# The iteration floor keeps a stray pre-OS packet (a UEFI netboot attempt) from
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# tripping the flip before the guest is even past its interrupt and timer setup.
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wait_net_up() {
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local base=$1 i=0
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for _ in $(seq 1 100); do # ~300 s cap, then raise anyway if still up
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i=$((i + 1))
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running || return 1
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[ "$i" -ge 4 ] && [ -n "$tap" ] && [ -r "$RX" ] &&
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[ "$(rx)" -ge "$((base + 4))" ] && return 0
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sleep 3
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done
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return 0
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}
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# The hook arms this watcher at prepare, before QEMU starts, so the domain is not
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# yet running and its tap does not exist. Wait for the domain, then read the tap;
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# otherwise the first running check in wait_net_up bails and the flip never happens.
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for _ in $(seq 1 120); do running && break; sleep 1; done
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running || exit 0
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tap=$($V domiflist "$DOMAIN" 2>/dev/null | awk '$1 ~ /^(vnet|tap|macvtap)/ {print $1; exit}')
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RX="/sys/class/net/$tap/statistics/rx_packets"
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# initial cold boot: wait for the network, then harden
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wait_net_up 0
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running || exit 0
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set_Y
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logger -t vfio-cpuid "$DOMAIN network up: cpuid_passthrough=Y"
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# every in-guest reboot fires a QEMU RESET: drop to N for the re-enumeration, then
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# raise it again once the guest's NIC is back. --loop streams one line per reset.
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$V qemu-monitor-event --domain "$DOMAIN" --event RESET --loop 2>/dev/null | while read -r _; do
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running || continue
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base=$(rx)
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set_N
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logger -t vfio-cpuid "$DOMAIN reset: cpuid_passthrough=N for re-enumeration"
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wait_net_up "$base" || continue
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running || continue
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set_Y
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logger -t vfio-cpuid "$DOMAIN back up: cpuid_passthrough=Y"
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done
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