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Shutemov" To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen Cc: x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Andi Kleen , Sean Christopherson Subject: [PATCH] x86/trampoline: Bypass compat mode in trampoline_start64() if not needed Date: Sat, 6 Jan 2024 04:01:06 +0300 Message-ID: <20240106010106.25772-1-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.41.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1787300834265038026 X-GMAIL-MSGID: 1787300834265038026 The trampoline_start64() vector is used when a secondary CPU starts in 64-bit mode. The current implementation directly enters compatibility mode. It is necessary to disable paging and re-enable it in the correct paging mode: either 4- or 5-level, depending on the configuration. The X86S[1] ISA does not support compatibility mode in ring 0, and paging cannot be disabled. The trampoline_start64() function is reworked to only enter compatibility mode if it is necessary to change the paging mode. If the CPU is already in the desired paging mode, it will proceed in long mode. This change will allow a secondary CPU to boot on an X86S machine as long as the CPU is already in the correct paging mode. In the future, there will be a mechanism to switch between paging modes without disabling paging. [1] https://www.intel.com/content/www/us/en/developer/articles/technical/envisioning-future-simplified-architecture.html Signed-off-by: Kirill A. Shutemov Reviewed-by: Andi Kleen Cc: Sean Christopherson --- arch/x86/realmode/rm/trampoline_64.S | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S index c9f76fae902e..70c6dff658e6 100644 --- a/arch/x86/realmode/rm/trampoline_64.S +++ b/arch/x86/realmode/rm/trampoline_64.S @@ -220,6 +220,33 @@ SYM_CODE_START(trampoline_start64) lidt tr_idt(%rip) lgdt tr_gdt64(%rip) + /* Check if paging mode has to be changed */ + movq %cr4, %rax + xorq pa_tr_cr4, %rax + andq $X86_CR4_LA57, %rax + jnz .L_switch_paging + + /* Paging mode is correct proceed in 64-bit mode */ + + LOCK_AND_LOAD_REALMODE_ESP lock_pa=1 + + movw $__KERNEL_DS, %dx + movl %edx, %ss + addl $pa_real_mode_base, %esp + movl %edx, %ds + movl %edx, %es + movl %edx, %fs + movl %edx, %gs + + movl $pa_trampoline_pgd, %eax + movq %rax, %cr3 + + jmpq *tr_start(%rip) +.L_switch_paging: + /* + * To switch between 4- and 5-level paging modes, it is necessary + * to disable paging. This must be done in the compatibility mode. + */ ljmpl *tr_compat(%rip) SYM_CODE_END(trampoline_start64)