linux-kernel - [PATCH 1/3] riscv: Don't use va_pa

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Message-Id: <20211126180411.187597-1-mick@ics.forth.gr>
Date:   Fri, 26 Nov 2021 20:04:09 +0200
From:   Nick Kossifidis <mick@....forth.gr>
To:     palmer@...belt.com, paul.walmsley@...ive.com, aou@...s.berkeley.edu
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Nick Kossifidis <mick@....forth.gr>,
        Alexandre Ghiti <alex@...ti.fr>, stable@...r.kernel.org
Subject: [PATCH 1/3] riscv: Don't use va_pa_offset on kdump

On kdump instead of using an intermediate step to relocate the kernel,
that lives in a "control buffer" outside the current kernel's mapping,
we jump to the crash kernel directly by calling riscv_kexec_norelocate().
The current implementation uses va_pa_offset while switching to physical
addressing, however since we moved the kernel outside the linear mapping
this won't work anymore since riscv_kexec_norelocate() is part of the
kernel mapping and we should use kernel_map.va_kernel_pa_offset, and also
take XIP kernel into account.

We don't really need to use va_pa_offset on riscv_kexec_norelocate, we
can just set STVEC to the physical address of the new kernel instead and
let the hart jump to the new kernel on the next instruction after setting
SATP to zero. This fixes kdump and is also simpler/cleaner.

I tested this on the latest qemu and HiFive Unmatched and works as
expected.

v2: I removed the direct jump after setting satp as suggested.

Fixes: 2bfc6cd81bd1 ("riscv: Move kernel mapping outside of linear mapping")

Signed-off-by: Nick Kossifidis <mick@....forth.gr>
Reviewed-by: Alexandre Ghiti <alex@...ti.fr>
Cc: <stable@...r.kernel.org> # 5.13
Cc: <stable@...r.kernel.org> # 5.14
---
 arch/riscv/kernel/kexec_relocate.S | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/kernel/kexec_relocate.S b/arch/riscv/kernel/kexec_relocate.S
index a80b52a74..059c5e216 100644
--- a/arch/riscv/kernel/kexec_relocate.S
+++ b/arch/riscv/kernel/kexec_relocate.S
@@ -159,25 +159,15 @@ SYM_CODE_START(riscv_kexec_norelocate)
 	 * s0: (const) Phys address to jump to
 	 * s1: (const) Phys address of the FDT image
 	 * s2: (const) The hartid of the current hart
-	 * s3: (const) kernel_map.va_pa_offset, used when switching MMU off
 	 */
 	mv	s0, a1
 	mv	s1, a2
 	mv	s2, a3
-	mv	s3, a4

 	/* Disable / cleanup interrupts */
 	csrw	CSR_SIE, zero
 	csrw	CSR_SIP, zero

-	/* Switch to physical addressing */
-	la	s4, 1f
-	sub	s4, s4, s3
-	csrw	CSR_STVEC, s4
-	csrw	CSR_SATP, zero
-
-.align 2
-1:
 	/* Pass the arguments to the next kernel  / Cleanup*/
 	mv	a0, s2
 	mv	a1, s1
@@ -214,7 +204,15 @@ SYM_CODE_START(riscv_kexec_norelocate)
 	csrw	CSR_SCAUSE, zero
 	csrw	CSR_SSCRATCH, zero

-	jalr	zero, a2, 0
+	/*
+	 * Switch to physical addressing
+	 * This will also trigger a jump to CSR_STVEC
+	 * which in this case is the address of the new
+	 * kernel.
+	 */
+	csrw	CSR_STVEC, a2
+	csrw	CSR_SATP, zero
+
 SYM_CODE_END(riscv_kexec_norelocate)

 .section ".rodata"
-- 
2.32.0