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([185.25.67.249]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c5cf49de00sm1498937a12.55.2024.09.24.23.01.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Sep 2024 23:01:15 -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: 955e1273-7b03-11ef-a0ba-8be0dac302b0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloud.com; s=cloud; t=1727244078; x=1727848878; 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=kPTBonMqIKr1Gh1WSmKkngmOhz6efABUMJImPAurUOk=; b=aXLjztczSTa3ba2gYWA7jzQvb/f8e3Gcrna5kr87EffZUZD5lUvhxzK5SSx0mHx1YK trvN4H6W9BYsL33YDEu3NlRv+IZ3S53XvuSrkEJV8G3/04zfXnFm5fXGXkZouxpQjVT4 iLf+zKqdJWXXKVd0rcnMMkARYjsheCE1CFc7s= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727244078; x=1727848878; 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=kPTBonMqIKr1Gh1WSmKkngmOhz6efABUMJImPAurUOk=; b=TLcWrbnEin53ffjXlYi9v5C1Lp4ecqS0bbjg3n5YaS/7T77ALwb8TnPS6dCit7CTPU JwzYETD+R8EHeTJ0juH51AxuERSpvWLGOd16HP1tVgnnlE5kG4C2Y3TxjxGoAvL0M5W4 OFrnh7TU1AD04xm3gcoAp8I4QIcah/6YvKdyiDbck9jf/DgpoIlFrdY/ppAZflrFXEpE GNxUoYw3PRa5zVDYdyGbEfSzlJC97MfGqROGB9uZ7BdRSmwMz599FOtN6pii23NITC8n Mx7yokQ/YcwCCKDYmaBXG7oLCNIUyh3+skY1agd65suihcDj/ySzW8RJspn3d7BZP1BG ziuQ== X-Gm-Message-State: AOJu0YxX7nN6XBTybmlumtFbKd0UBrTKNxNzteqXLcGcu8/GTpZTbX8k LYvLOKtrNqduei8IyU6yiu3A5vnxdgzkoaD2zs7ZoL88RbO4PAI8mnSHhujWkzudbuh8G1hrzh6 p X-Google-Smtp-Source: AGHT+IGfxAPkHF82/MgXoJ0SIUMRhoH0ZoSo/6R1zTW8wQLGgoZoF07X2qgHKuSEX7bfmgdR477DDg== X-Received: by 2002:a05:6512:e8c:b0:533:4817:7280 with SMTP id 2adb3069b0e04-53877537533mr856227e87.35.1727244077586; Tue, 24 Sep 2024 23:01:17 -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 v4 2/4] x86/boot: Refactor BIOS/PVH start Date: Wed, 25 Sep 2024 07:00:59 +0100 Message-Id: <20240925060101.259244-3-frediano.ziglio@cloud.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240925060101.259244-1-frediano.ziglio@cloud.com> References: <20240925060101.259244-1-frediano.ziglio@cloud.com> MIME-Version: 1.0 The 2 code paths were sharing quite some common code, reuse it instead of having duplications. Use %dl register to store boot type before running common code. Using a 8 bit register reduces code size. 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. --- xen/arch/x86/boot/head.S | 108 +++++++++++++++------------------------ 1 file changed, 40 insertions(+), 68 deletions(-) diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S index 267207e5a2..2d2f56ad22 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 (%ebx), %eax /* mov $XEN_HVM_START_MAGIC_VALUE, %eax */ + /* + * Fall through into BIOS code. + * We will use %eax to distinguish we came from PHV 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. + * + * Durig 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) @@ -449,62 +458,40 @@ __pvh_start: mov %ecx, %es mov %ecx, %ss - /* Skip bootloader setup and bios setup, go straight to trampoline */ - movb $1, sym_esi(pvh_boot) - movb $1, sym_esi(skip_realmode) + /* Load null selector to unused segment registers. */ + xor %ecx, %ecx + mov %ecx, %fs + mov %ecx, %gs - /* 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 - lea sym_esi(__bss_start), %edi lea sym_esi(__bss_end), %ecx sub %edi, %ecx xor %eax, %eax shr $2, %ecx 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) + mov (%ebx), %eax /* mov $XEN_HVM_START_MAGIC_VALUE, %eax */ + 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 +550,7 @@ __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 */