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target/ppc: Avoid warning message for zero process table entries

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A translation that encounters a process table entry that is zero is
something that Linux does to cause certain kernel NULL pointer
dereferences to fault. It is not itself a programming error, so avoid
the guest error log.

Message-ID: <20241219034035.1826173-5-npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
This commit is contained in:
Nicholas Piggin 2024-12-19 13:40:34 +10:00
parent d8a624515a
commit b4aa82dc3a
1 changed files with 14 additions and 0 deletions
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14
target/ppc/mmu-radix64.c
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@ -571,6 +571,20 @@ static int ppc_radix64_process_scoped_xlate(PowerPCCPU *cpu,
prtbe0 = ldq_phys(cs->as, h_raddr);
}
/*
* Some Linux uses a zero process table entry in PID!=0 for kernel context
* without userspace in order to fault on NULL dereference, because using
* PIDR=0 for the kernel causes the Q0 page table to be used to translate
* Q3 as well. Check for that case here to avoid the invalid configuration
* message.
*/
if (unlikely(!prtbe0)) {
if (guest_visible) {
ppc_radix64_raise_si(cpu, access_type, eaddr, DSISR_R_BADCONFIG);
}
return 1;
}
/* Walk Radix Tree from Process Table Entry to Convert EA to RA */
*g_page_size = PRTBE_R_GET_RTS(prtbe0);
base_addr = prtbe0 & PRTBE_R_RPDB;