linux-kernel - [PATCH v2 3/4] x86/mm: Flush global TLB when switching to trampoline page-table

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Message-Id: <20210929145501.4612-4-joro@8bytes.org>
Date:   Wed, 29 Sep 2021 16:55:00 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <jroedel@...e.de>,
        Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/4] x86/mm: Flush global TLB when switching to trampoline page-table

From: Joerg Roedel <jroedel@...e.de>

Move the switching code into a function so that it can be re-used and
add a global TLB flush. This makes sure that usage of memory which is
not mapped in the trampoline page-table is reliably caught.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/include/asm/realmode.h |  1 +
 arch/x86/kernel/reboot.c        | 12 ++----------
 arch/x86/realmode/init.c        | 19 +++++++++++++++++++
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 5db5d083c873..331474b150f1 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -89,6 +89,7 @@ static inline void set_real_mode_mem(phys_addr_t mem)
 }
 
 void reserve_real_mode(void);
+void load_trampoline_pgtable(void);
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 0a40df66a40d..fa700b46588e 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -113,17 +113,9 @@ void __noreturn machine_real_restart(unsigned int type)
 	spin_unlock(&rtc_lock);
 
 	/*
-	 * Switch back to the initial page table.
+	 * Switch to the trampoline page table.
 	 */
-#ifdef CONFIG_X86_32
-	load_cr3(initial_page_table);
-#else
-	write_cr3(real_mode_header->trampoline_pgd);
-
-	/* Exiting long mode will fail if CR4.PCIDE is set. */
-	if (boot_cpu_has(X86_FEATURE_PCID))
-		cr4_clear_bits(X86_CR4_PCIDE);
-#endif
+	load_trampoline_pgtable();
 
 	/* Jump to the identity-mapped low memory code */
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 31b5856010cb..0cfe1046cec9 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -17,6 +17,25 @@ u32 *trampoline_cr4_features;
 /* Hold the pgd entry used on booting additional CPUs */
 pgd_t trampoline_pgd_entry;
 
+void load_trampoline_pgtable(void)
+{
+#ifdef CONFIG_X86_32
+	load_cr3(initial_page_table);
+#else
+	/* Exiting long mode will fail if CR4.PCIDE is set. */
+	if (boot_cpu_has(X86_FEATURE_PCID))
+		cr4_clear_bits(X86_CR4_PCIDE);
+
+	write_cr3(real_mode_header->trampoline_pgd);
+#endif
+
+	/*
+	 * Flush global TLB entries to catch any bugs where code running on the
+	 * trampoline_pgd uses memory not mapped into the trampoline page-table.
+	 */
+	__flush_tlb_all();
+}
+
 void __init reserve_real_mode(void)
 {
 	phys_addr_t mem;
-- 
2.33.0