KVM: SVM: Skip fastpath emulation on VM-Exit if next RIP isn't valid

In the Linux kernel, the following vulnerability has been resolved:

KVM: SVM: Skip fastpath emulation on VM-Exit if next RIP isn't valid

Skip the WRMSR and HLT fastpaths in SVM's VM-Exit handler if the next RIP
isn't valid, e.g. because KVM is running with nrips=false. SVM must
decode and emulate to skip the instruction if the CPU doesn't provide the
next RIP, and getting the instruction bytes to decode requires reading
guest memory. Reading guest memory through the emulator can fault, i.e.
can sleep, which is disallowed since the fastpath handlers run with IRQs
disabled.

BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:106
in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 32611, name: qemu
preempt_count: 1, expected: 0
INFO: lockdep is turned off.
irq event stamp: 30580
hardirqs last enabled at (30579): [<ffffffffc08b2527>] vcpu_run+0x1787/0x1db0 [kvm]
hardirqs last disabled at (30580): [<ffffffffb4f62e32>] __schedule+0x1e2/0xed0
softirqs last enabled at (30570): [<ffffffffb4247a64>] fpu_swap_kvm_fpstate+0x44/0x210
softirqs last disabled at (30568): [<ffffffffb4247a64>] fpu_swap_kvm_fpstate+0x44/0x210
CPU: 298 UID: 0 PID: 32611 Comm: qemu Tainted: G U 6.16.0-smp--e6c618b51cfe-sleep #782 NONE
Tainted: [U]=USER
Hardware name: Google Astoria-Turin/astoria, BIOS 0.20241223.2-0 01/17/2025
Call Trace:
<TASK>
dump_stack_lvl+0x7d/0xb0
__might_resched+0x271/0x290
__might_fault+0x28/0x80
kvm_vcpu_read_guest_page+0x8d/0xc0 [kvm]
kvm_fetch_guest_virt+0x92/0xc0 [kvm]
__do_insn_fetch_bytes+0xf3/0x1e0 [kvm]
x86_decode_insn+0xd1/0x1010 [kvm]
x86_emulate_instruction+0x105/0x810 [kvm]
__svm_skip_emulated_instruction+0xc4/0x140 [kvm_amd]
handle_fastpath_invd+0xc4/0x1a0 [kvm]
vcpu_run+0x11a1/0x1db0 [kvm]
kvm_arch_vcpu_ioctl_run+0x5cc/0x730 [kvm]
kvm_vcpu_ioctl+0x578/0x6a0 [kvm]
__se_sys_ioctl+0x6d/0xb0
do_syscall_64+0x8a/0x2c0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7f479d57a94b
</TASK>

Note, this is essentially a reapply of commit 5c30e8101e8d ("KVM: SVM:
Skip WRMSR fastpath on VM-Exit if next RIP isn't valid"), but with
different justification (KVM now grabs SRCU when skipping the instruction
for other reasons).