riscv: Fix IPIs usage in kfence_protect_page()

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

riscv: Fix IPIs usage in kfence_protect_page()

flush_tlb_kernel_range() may use IPIs to flush the TLBs of all the

cores, which triggers the following warning when the irqs are disabled:

[ 3.455330] WARNING: CPU: 1 PID: 0 at kernel/smp.c:815 smp_call_function_many_cond+0x452/0x520

[ 3.456647] Modules linked in:

[ 3.457218] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.12.0-rc7-00010-g91d3de7240b8 #1

[ 3.457416] Hardware name: QEMU QEMU Virtual Machine, BIOS

[ 3.457633] epc : smp_call_function_many_cond+0x452/0x520

[ 3.457736] ra : on_each_cpu_cond_mask+0x1e/0x30

[ 3.457786] epc : ffffffff800b669a ra : ffffffff800b67c2 sp : ff2000000000bb50

[ 3.457824] gp : ffffffff815212b8 tp : ff6000008014f080 t0 : 000000000000003f

[ 3.457859] t1 : ffffffff815221e0 t2 : 000000000000000f s0 : ff2000000000bc10

[ 3.457920] s1 : 0000000000000040 a0 : ffffffff815221e0 a1 : 0000000000000001

[ 3.457953] a2 : 0000000000010000 a3 : 0000000000000003 a4 : 0000000000000000

[ 3.458006] a5 : 0000000000000000 a6 : ffffffffffffffff a7 : 0000000000000000

[ 3.458042] s2 : ffffffff815223be s3 : 00fffffffffff000 s4 : ff600001ffe38fc0

[ 3.458076] s5 : ff600001ff950d00 s6 : 0000000200000120 s7 : 0000000000000001

[ 3.458109] s8 : 0000000000000001 s9 : ff60000080841ef0 s10: 0000000000000001

[ 3.458141] s11: ffffffff81524812 t3 : 0000000000000001 t4 : ff60000080092bc0

[ 3.458172] t5 : 0000000000000000 t6 : ff200000000236d0

[ 3.458203] status: 0000000200000100 badaddr: ffffffff800b669a cause: 0000000000000003

[ 3.458373] [<ffffffff800b669a>] smp_call_function_many_cond+0x452/0x520

[ 3.458593] [<ffffffff800b67c2>] on_each_cpu_cond_mask+0x1e/0x30

[ 3.458625] [<ffffffff8000e4ca>] __flush_tlb_range+0x118/0x1ca

[ 3.458656] [<ffffffff8000e6b2>] flush_tlb_kernel_range+0x1e/0x26

[ 3.458683] [<ffffffff801ea56a>] kfence_protect+0xc0/0xce

[ 3.458717] [<ffffffff801e9456>] kfence_guarded_free+0xc6/0x1c0

[ 3.458742] [<ffffffff801e9d6c>] __kfence_free+0x62/0xc6

[ 3.458764] [<ffffffff801c57d8>] kfree+0x106/0x32c

[ 3.458786] [<ffffffff80588cf2>] detach_buf_split+0x188/0x1a8

[ 3.458816] [<ffffffff8058708c>] virtqueue_get_buf_ctx+0xb6/0x1f6

[ 3.458839] [<ffffffff805871da>] virtqueue_get_buf+0xe/0x16

[ 3.458880] [<ffffffff80613d6a>] virtblk_done+0x5c/0xe2

[ 3.458908] [<ffffffff8058766e>] vring_interrupt+0x6a/0x74

[ 3.458930] [<ffffffff800747d8>] __handle_irq_event_percpu+0x7c/0xe2

[ 3.458956] [<ffffffff800748f0>] handle_irq_event+0x3c/0x86

[ 3.458978] [<ffffffff800786cc>] handle_simple_irq+0x9e/0xbe

[ 3.459004] [<ffffffff80073934>] generic_handle_domain_irq+0x1c/0x2a

[ 3.459027] [<ffffffff804bf87c>] imsic_handle_irq+0xba/0x120

[ 3.459056] [<ffffffff80073934>] generic_handle_domain_irq+0x1c/0x2a

[ 3.459080] [<ffffffff804bdb76>] riscv_intc_aia_irq+0x24/0x34

[ 3.459103] [<ffffffff809d0452>] handle_riscv_irq+0x2e/0x4c

[ 3.459133] [<ffffffff809d923e>] call_on_irq_stack+0x32/0x40

So only flush the local TLB and let the lazy kfence page fault handling

deal with the faults which could happen when a core has an old protected

pte version cached in its TLB. That leads to potential inaccuracies which

can be tolerated when using kfence.