Linux-RISC-V Archive on lore.kernel.org
 help / color / mirror / Atom feed
From: fangyu.yu@linux.alibaba.com
To: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu,
	alex@ghiti.fr, songshuaishuai@tinylab.org, bjorn@rivosinc.com,
	ardb@kernel.org, arnd@arndb.de, bhelgaas@google.com,
	richard.lyu@suse.com, tzimmermann@suse.de, nathan@kernel.org
Cc: guoren@kernel.org, kvm-riscv@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Fangyu Yu <fangyu.yu@linux.alibaba.com>
Subject: [PATCH 3/4] riscv: kexec: Build trampoline page tables for crash kernel entry
Date: Tue, 24 Mar 2026 19:45:26 +0800	[thread overview]
Message-ID: <20260324114527.91494-4-fangyu.yu@linux.alibaba.com> (raw)
In-Reply-To: <20260324114527.91494-1-fangyu.yu@linux.alibaba.com>

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

Crash kexec uses riscv_kexec_norelocate as a trampoline to jump into
the crashkernel. Add a small helper to build dedicated 4KB page tables
that map the trampoline page as executable.

Two mappings are installed:
  - VA(__kexec_tramp_text_start) -> PA(__kexec_tramp_text_start)
  - PA(__kexec_tramp_text_start) -> PA(__kexec_tramp_text_start)

This allows the trampoline to run regardless of whether it is entered
via its linked virtual address or its physical address.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
 arch/riscv/kernel/machine_kexec.c | 103 +++++++++++++++++++++++++++++-
 1 file changed, 102 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
index 2306ce3e5f22..4e522a64a614 100644
--- a/arch/riscv/kernel/machine_kexec.c
+++ b/arch/riscv/kernel/machine_kexec.c
@@ -18,6 +18,98 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 
+static pgd_t kexec_tramp_pgd[PTRS_PER_PGD] __aligned(PAGE_SIZE);
+static p4d_t kexec_tramp_p4d[PTRS_PER_P4D] __aligned(PAGE_SIZE);
+static pud_t kexec_tramp_pud[PTRS_PER_PUD] __aligned(PAGE_SIZE);
+static pmd_t kexec_tramp_pmd[PTRS_PER_PMD] __aligned(PAGE_SIZE);
+static pte_t kexec_tramp_pte[PTRS_PER_PTE] __aligned(PAGE_SIZE);
+static p4d_t kexec_tramp_p4d2[PTRS_PER_P4D] __aligned(PAGE_SIZE);
+static pud_t kexec_tramp_pud2[PTRS_PER_PUD] __aligned(PAGE_SIZE);
+static pmd_t kexec_tramp_pmd2[PTRS_PER_PMD] __aligned(PAGE_SIZE);
+static pte_t kexec_tramp_pte2[PTRS_PER_PTE] __aligned(PAGE_SIZE);
+
+static void riscv_kexec_build_tramp(unsigned long va, unsigned long pa)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	p4d_t *p4d;
+	pmd_t *pmd;
+	pte_t *pte;
+	int index;
+
+	index = pgd_index(va);
+	pgd = (pgd_t *)kexec_tramp_pgd + index;
+	if (pgtable_l5_enabled)
+		set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa_symbol(kexec_tramp_p4d)),
+			PAGE_TABLE));
+	else
+		set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa_symbol(kexec_tramp_pud)),
+			PAGE_TABLE));
+
+	if (pgtable_l5_enabled) {
+		index = p4d_index(va);
+		p4d = (p4d_t *)kexec_tramp_p4d + index;
+		if (pgtable_l4_enabled)
+			set_p4d(p4d, pfn_p4d(PFN_DOWN(__pa_symbol(kexec_tramp_pud)),
+				PAGE_TABLE));
+		else
+			set_p4d(p4d, pfn_p4d(PFN_DOWN(__pa_symbol(kexec_tramp_pmd)),
+				PAGE_TABLE));
+	}
+
+	if (pgtable_l4_enabled) {
+		index = pud_index(va);
+		pud = (pud_t *)kexec_tramp_pud + index;
+		set_pud(pud, pfn_pud(PFN_DOWN(__pa_symbol(kexec_tramp_pmd)), PAGE_TABLE));
+	}
+
+	index = pmd_index(va);
+	if (pgtable_l4_enabled)
+		pmd = (pmd_t *)kexec_tramp_pmd + index;
+	else
+		pmd = (pmd_t *)kexec_tramp_pud + index;
+	set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa_symbol(kexec_tramp_pte)), PAGE_TABLE));
+
+	index = pte_index(va);
+	pte = (pte_t *)kexec_tramp_pte + index;
+	set_pte(pte, pfn_pte(PFN_DOWN(pa), PAGE_KERNEL_EXEC));
+
+	index = pgd_index(pa);
+	pgd = (pgd_t *)kexec_tramp_pgd + index;
+	if (pgtable_l5_enabled)
+		set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa_symbol(kexec_tramp_p4d2)), PAGE_TABLE));
+	else
+		set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa_symbol(kexec_tramp_pud2)), PAGE_TABLE));
+
+	if (pgtable_l5_enabled) {
+		index = p4d_index(pa);
+		p4d = (p4d_t *)kexec_tramp_p4d2 + index;
+		if (pgtable_l4_enabled)
+			set_p4d(p4d, pfn_p4d(PFN_DOWN(__pa_symbol(kexec_tramp_pud2)),
+				PAGE_TABLE));
+		else
+			set_p4d(p4d, pfn_p4d(PFN_DOWN(__pa_symbol(kexec_tramp_pmd2)),
+				PAGE_TABLE));
+	}
+
+	if (pgtable_l4_enabled) {
+		index = pud_index(pa);
+		pud = (pud_t *)kexec_tramp_pud2 + index;
+		set_pud(pud, pfn_pud(PFN_DOWN(__pa_symbol(kexec_tramp_pmd2)), PAGE_TABLE));
+	}
+
+	index = pmd_index(pa);
+	if (pgtable_l4_enabled)
+		pmd = (pmd_t *)kexec_tramp_pmd2 + index;
+	else
+		pmd = (pmd_t *)kexec_tramp_pud2 + index;
+	set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa_symbol(kexec_tramp_pte2)), PAGE_TABLE));
+
+	index = pte_index(pa);
+	pte = (pte_t *)kexec_tramp_pte2 + index;
+	set_pte(pte, pfn_pte(PFN_DOWN(pa), PAGE_KERNEL_EXEC));
+}
+
 /*
  * machine_kexec_prepare - Initialize kexec
  *
@@ -164,8 +256,17 @@ machine_kexec(struct kimage *image)
 
 	if (image->type != KEXEC_TYPE_CRASH)
 		kexec_method = control_code_buffer;
-	else
+	else {
 		kexec_method = (riscv_kexec_method) &riscv_kexec_norelocate;
+		/*
+		 * Build two 4KB identity-mapping page tables for the
+		 * trampoline page:
+		 *   - VA(__kexec_tramp_text_start) -> PA(__kexec_tramp_text_start)
+		 *   - PA(__kexec_tramp_text_start) -> PA(__kexec_tramp_text_start)
+		 */
+		riscv_kexec_build_tramp((unsigned long)__kexec_tramp_text_start,
+					__pa_symbol(__kexec_tramp_text_start));
+	}
 
 	pr_notice("Will call new kernel at %08lx from hart id %lx\n",
 		  jump_addr, this_hart_id);
-- 
2.50.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  parent reply	other threads:[~2026-03-24 11:46 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-24 11:45 [PATCH 0/4] Add crashdump support in guest kernel fangyu.yu
2026-03-24 11:45 ` [PATCH 1/4] riscv: Add kexec trampoline text section to vmlinux.lds.S fangyu.yu
2026-03-24 11:45 ` [PATCH 2/4] riscv: kexec: Place norelocate trampoline into .kexec.tramp.text fangyu.yu
2026-03-24 11:45 ` fangyu.yu [this message]
2026-03-24 11:45 ` [PATCH 4/4] riscv: kexec: Switch to trampoline page table before norelocate fangyu.yu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20260324114527.91494-4-fangyu.yu@linux.alibaba.com \
    --to=fangyu.yu@linux.alibaba.com \
    --cc=alex@ghiti.fr \
    --cc=aou@eecs.berkeley.edu \
    --cc=ardb@kernel.org \
    --cc=arnd@arndb.de \
    --cc=bhelgaas@google.com \
    --cc=bjorn@rivosinc.com \
    --cc=guoren@kernel.org \
    --cc=kvm-riscv@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=nathan@kernel.org \
    --cc=palmer@dabbelt.com \
    --cc=pjw@kernel.org \
    --cc=richard.lyu@suse.com \
    --cc=songshuaishuai@tinylab.org \
    --cc=tzimmermann@suse.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox