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([185.25.67.249]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9392f5485asm325846666b.88.2024.09.26.02.21.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Sep 2024 02:21:18 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: b09094a4-7be8-11ef-a0ba-8be0dac302b0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloud.com; s=cloud; t=1727342479; x=1727947279; darn=lists.xenproject.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=S70211ALl89jb/A0SZTofQwu7xG6yOycti6baccoONo=; b=daBAYndEcrveyMX8AhioSCe4VfZa0Tlh3xKSdUska8n4F+Grt/AG9OFoKtBSq5vNVM r/YejshtuU30wZHjEFehv/gZB9sYSnrCWiVJcY7Phl6JIttslDX/GhN9gD74ZPbmr/IG Gm3T71e4BaqHghmCOEK5A0ZZHTjOSK+83QywI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727342479; x=1727947279; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=S70211ALl89jb/A0SZTofQwu7xG6yOycti6baccoONo=; b=EdPfmRldHn2kA8WkAK1Hd2jQcxiVBuw5y6qw1ysdf5TgbWzNECRyz84zJRxYDgcOpH rGcprAbFmeSadUakywkjXncGOEaE70MyKM/m0BWjJh5hIJQe6Shi7zMH/81qspHJqrlu J/bvlrbebWfMTwXzY1qOxAPlYuoo2GQeGHQSmXS/lukVqYM7oeGLX2oKxR+y4vECfgAi MMzgzc/pOSBqDinR/dpgxkBmiyevpRxcQ4prx85DxHgJ8NiEVutyejUwndlYxDMuCKUN Klk9bgr1P+bDp4JlSLke24z5uHzID3Sf3AXZI2Mfpe2H8A7O0BDaC1I/QJnNDy6B3mtG SXtg== X-Gm-Message-State: AOJu0YwZ7DMuTghbxpmzoQ6PE4M/W/H/Ly72RbGlAJ0DIPPytCK4umL7 G+DrnlrNOUII1qTDKpVTO2i49KoxdUeUg2y7VQus+uownpggiFivD1r5f9/R2cB8j9+rKkWkbyZ J X-Google-Smtp-Source: AGHT+IEcf4/lScaVZLzpXZT3ERQ12hSbh7r2/s33qXGej6Pc+j/Dl2WVNUdpBrtZnBvLJhojXZrpww== X-Received: by 2002:a17:907:9728:b0:a90:34e8:6761 with SMTP id a640c23a62f3a-a93b157ccfbmr291353666b.6.1727342478808; Thu, 26 Sep 2024 02:21:18 -0700 (PDT) From: Frediano Ziglio To: xen-devel@lists.xenproject.org Cc: Frediano Ziglio , Jan Beulich , Andrew Cooper , =?utf-8?q?Roger_Pau_Monn=C3=A9?= Subject: [PATCH v6 1/3] x86/boot: Refactor BIOS/PVH start Date: Thu, 26 Sep 2024 10:21:07 +0100 Message-Id: <20240926092109.475271-2-frediano.ziglio@cloud.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240926092109.475271-1-frediano.ziglio@cloud.com> References: <20240926092109.475271-1-frediano.ziglio@cloud.com> MIME-Version: 1.0 The 2 code paths were sharing quite some common code, reuse it instead of having duplications. Signed-off-by: Frediano Ziglio --- Changes since v1: - use %dl instead of %ebp to reduce code size; - fold cli instruction; - update some comments. Changes since v3: - dropped %dl and constant, distinguish entry by magic. Changes since v4: - remove old sentence from commit message; - fixed a typo; - load XEN_HVM_START_MAGIC_VALUE constant directly; - set %fs and %gs as other segment registers; - remove some spurious line changes. Changes since v5: - fixed a typo. --- xen/arch/x86/boot/head.S | 104 ++++++++++++++------------------------- 1 file changed, 37 insertions(+), 67 deletions(-) diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S index 267207e5a2..e0901ee400 100644 --- a/xen/arch/x86/boot/head.S +++ b/xen/arch/x86/boot/head.S @@ -25,6 +25,8 @@ #define MB2_HT(name) (MULTIBOOT2_HEADER_TAG_##name) #define MB2_TT(name) (MULTIBOOT2_TAG_TYPE_##name) +#define XEN_HVM_START_MAGIC_VALUE 0x336ec578 + .macro mb2ht_args arg:req, args:vararg .long \arg .ifnb \args @@ -409,13 +411,27 @@ cs32_switch: ELFNOTE(Xen, XEN_ELFNOTE_PHYS32_ENTRY, .long sym_offs(__pvh_start)) __pvh_start: - cld + mov $XEN_HVM_START_MAGIC_VALUE, %eax + /* + * Fall through into BIOS code. + * We will use %eax to distinguish we came from PVH entry point. + */ +#endif /* CONFIG_PVH_GUEST */ + +__start: cli + cld /* - * We need one call (i.e. push) to determine the load address. See - * __start for a discussion on how to do this safely using the PVH - * info structure. + * Multiboot (both 1 and 2) and PVH specify the stack pointer as + * undefined. This is unhelpful for relocatable images, where one + * call (i.e. push) is required to calculate the image's load address. + * + * During BIOS boot, there is one area of memory we know about with + * reasonable confidence that it isn't overlapped by Xen, and that's + * the Multiboot info structure in %ebx. Use it as a temporary stack. + * + * During PVH boot use info structure in %ebx. */ /* Preserve the field we're about to clobber. */ @@ -433,14 +449,7 @@ __pvh_start: /* Set up stack. */ lea STACK_SIZE - CPUINFO_sizeof + sym_esi(cpu0_stack), %esp - call .Linitialise_bss - - mov %ebx, sym_esi(pvh_start_info_pa) - - /* Force xen console. Will revert to user choice in init code. */ - movb $-1, sym_esi(opt_console_xen) - - /* Prepare gdt and segments */ + /* Initialize GDTR and basic data segments. */ add %esi, sym_esi(gdt_boot_base) lgdt sym_esi(gdt_boot_descr) @@ -448,19 +457,9 @@ __pvh_start: mov %ecx, %ds mov %ecx, %es mov %ecx, %ss + mov %ecx, %fs + mov %ecx, %gs - /* Skip bootloader setup and bios setup, go straight to trampoline */ - movb $1, sym_esi(pvh_boot) - movb $1, sym_esi(skip_realmode) - - /* Set trampoline_phys to use mfn 1 to avoid having a mapping at VA 0 */ - movw $0x1000, sym_esi(trampoline_phys) - mov (%ebx), %eax /* mov $XEN_HVM_START_MAGIC_VALUE, %eax */ - jmp trampoline_setup - -#endif /* CONFIG_PVH_GUEST */ - -.Linitialise_bss: /* Initialise the BSS. Preserve %eax (BOOTLOADER_MAGIC). */ mov %eax, %ebp @@ -472,39 +471,25 @@ __pvh_start: rep stosl mov %ebp, %eax - ret - -__start: - cld - cli - - /* - * Multiboot (both 1 and 2) specify the stack pointer as undefined - * when entering in BIOS circumstances. This is unhelpful for - * relocatable images, where one call (i.e. push) is required to - * calculate the image's load address. - * - * This early in boot, there is one area of memory we know about with - * reasonable confidence that it isn't overlapped by Xen, and that's - * the Multiboot info structure in %ebx. Use it as a temporary stack. - */ - /* Preserve the field we're about to clobber. */ - mov (%ebx), %edx - lea 4(%ebx), %esp +#ifdef CONFIG_PVH_GUEST + cmp $XEN_HVM_START_MAGIC_VALUE, %eax + jne 1f - /* Calculate the load base address. */ - call 1f -1: pop %esi - sub $sym_offs(1b), %esi + mov %ebx, sym_esi(pvh_start_info_pa) - /* Restore the clobbered field. */ - mov %edx, (%ebx) + /* Force xen console. Will revert to user choice in init code. */ + movb $-1, sym_esi(opt_console_xen) - /* Set up stack. */ - lea STACK_SIZE - CPUINFO_sizeof + sym_esi(cpu0_stack), %esp + /* Skip bootloader setup and bios setup, go straight to trampoline */ + movb $1, sym_esi(pvh_boot) + movb $1, sym_esi(skip_realmode) - call .Linitialise_bss + /* Set trampoline_phys to use mfn 1 to avoid having a mapping at VA 0 */ + movl $PAGE_SIZE, sym_esi(trampoline_phys) + jmp trampoline_setup +1: +#endif /* CONFIG_PVH_GUEST */ /* Bootloaders may set multiboot{1,2}.mem_lower to a nonzero value. */ xor %edx,%edx @@ -563,22 +548,7 @@ __start: trampoline_bios_setup: /* * Called on legacy BIOS platforms only. - * - * Initialize GDTR and basic data segments. */ - add %esi,sym_esi(gdt_boot_base) - lgdt sym_esi(gdt_boot_descr) - - mov $BOOT_DS,%ecx - mov %ecx,%ds - mov %ecx,%es - mov %ecx,%ss - /* %esp is initialized later. */ - - /* Load null descriptor to unused segment registers. */ - xor %ecx,%ecx - mov %ecx,%fs - mov %ecx,%gs /* Set up trampoline segment 64k below EBDA */ movzwl 0x40e,%ecx /* EBDA segment */