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Date:   Sat,  2 Oct 2021 15:20:26 +0300
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>
Subject: [PATCH] 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.

Signed-off-by: Nick Kossifidis <mick@....forth.gr>
---
 arch/riscv/kernel/kexec_relocate.S | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/kernel/kexec_relocate.S b/arch/riscv/kernel/kexec_relocate.S
index a80b52a74..e2f34196e 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
@@ -214,6 +204,11 @@ SYM_CODE_START(riscv_kexec_norelocate)
 	csrw	CSR_SCAUSE, zero
 	csrw	CSR_SSCRATCH, zero
 
+	/* Switch to physical addressing */
+	csrw	CSR_STVEC, a2
+	csrw	CSR_SATP, zero
+
+	/* This will trigger a jump to CSR_STVEC anyway */
 	jalr	zero, a2, 0
 SYM_CODE_END(riscv_kexec_norelocate)
 
-- 
2.32.0

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