linux-kernel - Re: x86/amd late microcode thread loading slows down boot

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Message-ID: <20241118191605.GEZzuSdRMZ0CICHdcZ@fat_crate.local>
Date: Mon, 18 Nov 2024 20:16:05 +0100
From: Borislav Petkov <bp@...en8.de>
To: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Thomas De Schampheleire <thomas.de_schampheleire@...ia.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: x86/amd late microcode thread loading slows down boot

On Thu, Nov 14, 2024 at 12:03:41PM +0000, Andrew Cooper wrote:
> > +static inline void invlpg(unsigned long addr)
> > +{
> > +	asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
> 
> "invlpg %0" :: "m" (*(char *)addr) : "memory"
> 
> The compiler can usually do a better job than forcing it into a plain
> register.

I think it is pretty smart and DTRT regardless.

The diff is only comments - insns are the same.

--- /tmp/before	2024-11-18 20:11:08.942464511 +0100
+++ /tmp/after	2024-11-18 20:10:37.722620293 +0100
@@ -3,27 +3,27 @@
 	movl	%ebp, %esi	# psize, psize
 # arch/x86/kernel/cpu/microcode/amd.c:495: 		unsigned long p_addr_end = p_addr + psize - 1;
 	leaq	-1(%rbx,%rsi), %rax	#, p_addr_end
-# ./arch/x86/include/asm/tlb.h:39: 	asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
+# ./arch/x86/include/asm/tlb.h:39: 	asm volatile("invlpg %0" ::"m" (*(char *)addr) : "memory");
 #APP
 # 39 "./arch/x86/include/asm/tlb.h" 1
-	invlpg (%rbx)	# mc
+	invlpg (%rbx)	# MEM[(char *)_1]
 # 0 "" 2
 # arch/x86/kernel/cpu/microcode/amd.c:503: 		if (p_addr >> PAGE_SHIFT != p_addr_end >> PAGE_SHIFT)
 #NO_APP
-	movq	%rbx, %rcx	# mc, tmp110
+	movq	%rbx, %rcx	# mc, tmp111
 # arch/x86/kernel/cpu/microcode/amd.c:503: 		if (p_addr >> PAGE_SHIFT != p_addr_end >> PAGE_SHIFT)
-	movq	%rax, %rdx	# p_addr_end, tmp111
+	movq	%rax, %rdx	# p_addr_end, tmp112
 # arch/x86/kernel/cpu/microcode/amd.c:503: 		if (p_addr >> PAGE_SHIFT != p_addr_end >> PAGE_SHIFT)
-	shrq	$12, %rcx	#, tmp110
+	shrq	$12, %rcx	#, tmp111
 # arch/x86/kernel/cpu/microcode/amd.c:503: 		if (p_addr >> PAGE_SHIFT != p_addr_end >> PAGE_SHIFT)
-	shrq	$12, %rdx	#, tmp111
+	shrq	$12, %rdx	#, tmp112
 # arch/x86/kernel/cpu/microcode/amd.c:503: 		if (p_addr >> PAGE_SHIFT != p_addr_end >> PAGE_SHIFT)
-	cmpq	%rdx, %rcx	# tmp111, tmp110
+	cmpq	%rdx, %rcx	# tmp112, tmp111
 	je	.L5	#,
-# ./arch/x86/include/asm/tlb.h:39: 	asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
+# ./arch/x86/include/asm/tlb.h:39: 	asm volatile("invlpg %0" ::"m" (*(char *)addr) : "memory");
 #APP
 # 39 "./arch/x86/include/asm/tlb.h" 1
-	invlpg (%rax)	# p_addr_end
+	invlpg (%rax)	# *addr.16_25
 # 0 "" 2
 # ./arch/x86/include/asm/tlb.h:40: }
 #NO_APP

-- 
Regards/Gruss,
    Boris.

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