Commit 974555d6 authored by Fangyu Yu's avatar Fangyu Yu Committed by Anup Patel
Browse files

RISC-V: KVM: Fix guest page fault within HLV* instructions 



When executing HLV* instructions at the HS mode, a guest page fault
may occur when a g-stage page table migration between triggering the
virtual instruction exception and executing the HLV* instruction.

This may be a corner case, and one simpler way to handle this is to
re-execute the instruction where the virtual  instruction exception
occurred, and the guest page fault will be automatically handled.

Fixes: b91f0e4c ("RISC-V: KVM: Factor-out instruction emulation into separate sources")
Signed-off-by: default avatarFangyu Yu <fangyu.yu@linux.alibaba.com>
Reviewed-by: default avatarAnup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20251121133543.46822-1-fangyu.yu@linux.alibaba.com


Signed-off-by: default avatarAnup Patel <anup@brainfault.org>
parent df60cb2e

arch/riscv/kvm/vcpu_insn.c

+22 −0
Original line number Diff line number Diff line
@@ -298,6 +298,22 @@ static int system_opcode_insn(struct kvm_vcpu *vcpu, struct kvm_run *run, 
	return (rc <= 0) ? rc : 1;

}



static bool is_load_guest_page_fault(unsigned long scause)

{

	/**

	 * If a g-stage page fault occurs, the direct approach

	 * is to let the g-stage page fault handler handle it

	 * naturally, however, calling the g-stage page fault

	 * handler here seems rather strange.

	 * Considering this is a corner case, we can directly

	 * return to the guest and re-execute the same PC, this

	 * will trigger a g-stage page fault again and then the

	 * regular g-stage page fault handler will populate

	 * g-stage page table.

	 */

	return (scause == EXC_LOAD_GUEST_PAGE_FAULT);

}



/**

 * kvm_riscv_vcpu_virtual_insn -- Handle virtual instruction trap

 *
@@ -323,6 +339,8 @@ int kvm_riscv_vcpu_virtual_insn(struct kvm_vcpu *vcpu, struct kvm_run *run, 
							  ct->sepc,

							  &utrap);

			if (utrap.scause) {

				if (is_load_guest_page_fault(utrap.scause))

					return 1;

				utrap.sepc = ct->sepc;

				kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);

				return 1;
@@ -378,6 +396,8 @@ int kvm_riscv_vcpu_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run, 
		insn = kvm_riscv_vcpu_unpriv_read(vcpu, true, ct->sepc,

						  &utrap);

		if (utrap.scause) {

			if (is_load_guest_page_fault(utrap.scause))

				return 1;

			/* Redirect trap if we failed to read instruction */

			utrap.sepc = ct->sepc;

			kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
@@ -504,6 +524,8 @@ int kvm_riscv_vcpu_mmio_store(struct kvm_vcpu *vcpu, struct kvm_run *run, 
		insn = kvm_riscv_vcpu_unpriv_read(vcpu, true, ct->sepc,

						  &utrap);

		if (utrap.scause) {

			if (is_load_guest_page_fault(utrap.scause))

				return 1;

			/* Redirect trap if we failed to read instruction */

			utrap.sepc = ct->sepc;

			kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);