Commit b7326c01 authored by Ricardo Koller's avatar Ricardo Koller Committed by Marc Zyngier
Browse files

KVM: selftests: Complete x86_64/sync_regs_test ucall 



The guest in sync_regs_test does raw ucalls by directly accessing the
ucall IO port. It makes these ucalls without setting %rdi to a `struct
ucall`, which is what a ucall uses to pass messages.  The issue is that
if the host did a get_ucall (the receiver side), it would try to access
the `struct ucall` at %rdi=0 which would lead to an error ("No mapping
for vm virtual address, gva: 0x0").

This issue is currently benign as there is no get_ucall in
sync_regs_test; however, that will change in the next commit as it
changes the unhandled exception reporting mechanism to use ucalls.  In
that case, every vcpu_run is followed by a get_ucall to check if the
guest is trying to report an unhandled exception.

Fix this in advance by setting %rdi to a UCALL_NONE struct ucall for the
sync_regs_test guest.

Tested with gcc-[8,9,10], and clang-[9,11].

Signed-off-by: default avatarRicardo Koller <ricarkol@google.com>
Reviewed-by: default avatarAndrew Jones <drjones@redhat.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210611011020.3420067-3-ricarkol@google.com
parent b78f4a59

tools/testing/selftests/kvm/x86_64/sync_regs_test.c

+6 −1
Original line number Diff line number Diff line
@@ -24,6 +24,10 @@ 


#define UCALL_PIO_PORT ((uint16_t)0x1000)



struct ucall uc_none = {

	.cmd = UCALL_NONE,

};



/*

 * ucall is embedded here to protect against compiler reshuffling registers

 * before calling a function. In this test we only need to get KVM_EXIT_IO
@@ -34,7 +38,8 @@ void guest_code(void) 
	asm volatile("1: in %[port], %%al\n"

		     "add $0x1, %%rbx\n"

		     "jmp 1b"

		     : : [port] "d" (UCALL_PIO_PORT) : "rax", "rbx");

		     : : [port] "d" (UCALL_PIO_PORT), "D" (&uc_none)

		     : "rax", "rbx");

}



static void compare_regs(struct kvm_regs *left, struct kvm_regs *right)