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Windows for ARM(64) on a6lte-kvm

PMU

EDK II and Windows ARM require the following registers to be trapped and emulated in sys_regs.c:

root@localhost:~# cat /proc/kmsg | grep "sys_regs"
[EDK II bootup]
<7>[ 1830.070417]  [0:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.070447]  [0:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.550467]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 2, CRm = 0, Op2 = 2, Rt = 0, is_write = 1
<7>[ 1830.550510]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 2, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.551762]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 10, CRm = 2, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.551778]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.551794]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.551809]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.551824]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
<7>[ 1830.551839]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 1, CRm = 0, Op2 = 0, Rt = 0, is_write = 1
[After manually load bootaa64.efi]
<7>[ 2293.777493]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0, Rt = 8, is_write = 0  => PMCCNTR_EL0
<7>[ 2293.777546]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 12, Op2 = 0, Rt = 8, is_write = 0  => PMCR_EL0
<7>[ 2293.777571]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 12, Op2 = 2, Rt = 10, is_write = 1 => PMCNTENCLR_EL0
<7>[ 2293.777595]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 12, Op2 = 3, Rt = 8, is_write = 1  => PMOVSCLR_EL0   (unimplemented)
<7>[ 2293.777617]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 0, CRn = 9, CRm = 14, Op2 = 2, Rt = 10, is_write = 1 => PMINTENCLR_EL1 (unimplemented)
<7>[ 2293.777639]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 12, Op2 = 0, Rt = 8, is_write = 1  => PMCR_EL0
<7>[ 2293.777661]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 14, CRm = 15, Op2 = 7, Rt = 9, is_write = 1 => PMCCFILTR_EL0
<7>[ 2293.777708]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 12, Op2 = 1, Rt = 8, is_write = 1  => PMCNTENSET_EL0
<7>[ 2293.777738]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 14, Op2 = 0, Rt = 9, is_write = 1  => PMUSERENR_EL0  (unimplemented)
<7>[ 2293.781100]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0, Rt = 20, is_write = 0 => PMCCNTR_EL0
<7>[ 2293.782409]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0, Rt = 19, is_write = 0 => PMCCNTR_EL0
<7>[ 2293.791457]  [2:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0, Rt = 8, is_write = 0  => PMCCNTR_EL0
<7>[ 2293.795274]  [3:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0, Rt = 19, is_write = 0 => PMCCNTR_EL0
<7>[ 2294.109411]  [3:qemu-system-aar: 6889] KVM sys_regs trap: Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0, Rt = 8, is_write = 0  => PMCCNTR_EL0

Note that the log's value is in decimal (output with %d), not hex! I also added some notes to make it easier to understand which register is being trapped.
The above log is generated inserting a simple prink to this line in the code:

int kvm_handle_sys_reg(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
	struct sys_reg_params params;
	unsigned long esr = kvm_vcpu_get_hsr(vcpu);

	params.is_aarch32 = false;
	params.is_32bit = false;
	params.Op0 = (esr >> 20) & 3;
	params.Op1 = (esr >> 14) & 0x7;
	params.CRn = (esr >> 10) & 0xf;
	params.CRm = (esr >> 1) & 0xf;
	params.Op2 = (esr >> 17) & 0x7;
	params.Rt = (esr >> 5) & 0x1f;
	params.is_write = !(esr & 1);

	// Stupid printk for debugging trap-and-emulate process
	printk(KERN_DEBUG "KVM sys_regs trap: Op0 = %d, Op1 = %d, CRn = %d, CRm = %d, Op2 = %d, Rt = %d, is_write = %d\n", params.Op0, params.Op1, params.CRn, params.CRm, params.Op2, params.Rt, params.is_write);

	return emulate_sys_reg(vcpu, &params);
}

Remember to

#include <linux/kern_levels.h>

or your compiler will complain!

I also wrote a simple Python script for converting the log to strings which can be used to find the line that the registers is trapped in sys_regs.c:

def trap(s):
	a = s.split(", ")
	b = []

	Op0 = int(a[0].split(" = ")[1])
	b.append("Op0(0b" + f'{Op0:02b}' + ")")

	Op1 = int(a[1].split(" = ")[1])
	b.append("Op1(0b" + f'{Op1:03b}' + ")")

	CRn = int(a[2].split(" = ")[1])
	b.append("CRn(0b" + f'{CRn:04b}' + ")")

	CRm = int(a[3].split(" = ")[1])
	b.append("CRm(0b" + f'{CRm:04b}' + ")")

	Op2 = int(a[4].split(" = ")[1])
	b.append("Op2(0b" + f'{Op2:03b}' + ")")

	return ', '.join(b)

Save it at trap.py. Then open your Python console, run:

>>> import trap
>>> trap.trap("Op0 = 3, Op1 = 3, CRn = 9, CRm = 13, Op2 = 0")
'Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1101), Op2(0b000)'
>>>

Replace the string passed to trap.trap() to the line you want to convert. Then open sys_regs.c, use CTRL+F and paste the converted string to search.

Link to registers trap code:

Register name and trap code Description ARM document link Implement status
PMCCNTR_EL0 Performance Monitors Cycle Count Register Link Implemented
PMCR_EL0 Performance Monitors Control Register Link Implemented
PMCNTENCLR_EL0 Performance Monitors Count Enable Clear register Link Implemented
PMOVSCLR_EL0 Performance Monitors Overflow Flag Status Clear Register Link Unimplemented
PMINTENCLR_EL1 Performance Monitors Interrupt Enable Clear register Link Unimplemented
PMCCFILTR_EL0 Performance Monitors Cycle Count Filter Register Link Implemented
PMCNTENSET_EL0 Performance Monitors Count Enable Set register Link Implemented
PMUSERENR_EL0 Performance Monitors User Enable Register Link Unimplemented

The process is being made at the pmu branch and will soon be merged back to main branch when it finished.
You can help us to make the work faster by sending pull requests! Thank you!

Consider seeing this mail thread