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Wed, 18 Dec 2024 19:40:54 -0800 (PST)
From: Nicholas Piggin <npiggin@gmail.com>
To: qemu-ppc@nongnu.org
Cc: Nicholas Piggin <npiggin@gmail.com>,
Daniel Henrique Barboza <danielhb413@gmail.com>,
Harsh Prateek Bora <harshpb@linux.ibm.com>, qemu-devel@nongnu.org
Subject: [PATCH 4/5] target/ppc: Avoid warning message for zero process table
entries
Date: Thu, 19 Dec 2024 13:40:34 +1000
Message-ID: <20241219034035.1826173-5-npiggin@gmail.com>
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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.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
target/ppc/mmu-radix64.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/target/ppc/mmu-radix64.c b/target/ppc/mmu-radix64.c
index be7a45f2549..02099300358 100644
--- a/target/ppc/mmu-radix64.c
+++ b/target/ppc/mmu-radix64.c
@@ -571,6 +571,20 @@ static int ppc_radix64_process_scoped_xlate(PowerPCCPU=
*cpu,
prtbe0 =3D ldq_phys(cs->as, h_raddr);
}
=20
+ /*
+ * Some Linux uses a zero process table entry in PID!=3D0 for kernel c=
ontext
+ * without userspace in order to fault on NULL dereference, because us=
ing
+ * PIDR=3D0 for the kernel causes the Q0 page table to be used to tran=
slate
+ * Q3 as well. Check for that case here to avoid the invalid configura=
tion
+ * message.
+ */
+ if (unlikely(!prtbe0)) {
+ if (guest_visible) {
+ ppc_radix64_raise_si(cpu, access_type, eaddr, DSISR_R_BADCONFI=
G);
+ }
+ return 1;
+ }
+
/* Walk Radix Tree from Process Table Entry to Convert EA to RA */
*g_page_size =3D PRTBE_R_GET_RTS(prtbe0);
base_addr =3D prtbe0 & PRTBE_R_RPDB;
--=20
2.45.2