linux-kernel - [PATCH v5 2/6] arch/x86/kvm: Refactor tlbflush and l1d flush

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Message-ID: <20200504041343.9651-3-sblbir@amazon.com>
Date:   Mon, 4 May 2020 14:13:39 +1000
From:   Balbir Singh <sblbir@...zon.com>
To:     <tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
CC:     <jpoimboe@...hat.com>, <tony.luck@...el.com>,
        <keescook@...omium.org>, <benh@...nel.crashing.org>,
        <x86@...nel.org>, <dave.hansen@...el.com>,
        <thomas.lendacky@....com>, Balbir Singh <sblbir@...zon.com>
Subject: [PATCH v5 2/6] arch/x86/kvm: Refactor tlbflush and l1d flush

Refactor the existing assembly bits into smaller helper functions
and also abstract L1D_FLUSH into a helper function. Use these
functions in kvm for L1D flushing.

Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Balbir Singh <sblbir@...zon.com>
---
 arch/x86/include/asm/cacheflush.h |  3 ++
 arch/x86/kernel/l1d_flush.c       | 54 +++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/vmx.c            | 29 ++---------------
 3 files changed, 60 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
index bac56fcd9790..21cc3b28fa63 100644
--- a/arch/x86/include/asm/cacheflush.h
+++ b/arch/x86/include/asm/cacheflush.h
@@ -8,7 +8,10 @@
 
 #define L1D_CACHE_ORDER 4
 void clflush_cache_range(void *addr, unsigned int size);
+void l1d_flush_populate_tlb(void *l1d_flush_pages);
 void *l1d_flush_alloc_pages(void);
 void l1d_flush_cleanup_pages(void *l1d_flush_pages);
+void l1d_flush_sw(void *l1d_flush_pages);
+int l1d_flush_hw(void);
 
 #endif /* _ASM_X86_CACHEFLUSH_H */
diff --git a/arch/x86/kernel/l1d_flush.c b/arch/x86/kernel/l1d_flush.c
index d605878c8f28..5871794f890d 100644
--- a/arch/x86/kernel/l1d_flush.c
+++ b/arch/x86/kernel/l1d_flush.c
@@ -34,3 +34,57 @@ void l1d_flush_cleanup_pages(void *l1d_flush_pages)
 	free_pages((unsigned long)l1d_flush_pages, L1D_CACHE_ORDER);
 }
 EXPORT_SYMBOL_GPL(l1d_flush_cleanup_pages);
+
+/*
+ * Not all users of l1d flush would want to populate the TLB first
+ * split out the function so that callers can optionally flush the L1D
+ * cache via sw without prefetching the TLB.
+ */
+void l1d_flush_populate_tlb(void *l1d_flush_pages)
+{
+	int size = PAGE_SIZE << L1D_CACHE_ORDER;
+
+	asm volatile(
+		/* First ensure the pages are in the TLB */
+		"xorl	%%eax, %%eax\n"
+		".Lpopulate_tlb:\n\t"
+		"movzbl	(%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
+		"addl	$4096, %%eax\n\t"
+		"cmpl	%%eax, %[size]\n\t"
+		"jne	.Lpopulate_tlb\n\t"
+		"xorl	%%eax, %%eax\n\t"
+		"cpuid\n\t"
+		:: [flush_pages] "r" (l1d_flush_pages),
+		    [size] "r" (size)
+		: "eax", "ebx", "ecx", "edx");
+}
+EXPORT_SYMBOL_GPL(l1d_flush_populate_tlb);
+
+int l1d_flush_hw(void)
+{
+	if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) {
+		wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
+		return 0;
+	}
+	return -ENOTSUPP;
+}
+EXPORT_SYMBOL_GPL(l1d_flush_hw);
+
+void l1d_flush_sw(void *l1d_flush_pages)
+{
+	int size = PAGE_SIZE << L1D_CACHE_ORDER;
+
+	asm volatile(
+			/* Fill the cache */
+			"xorl	%%eax, %%eax\n"
+			".Lfill_cache:\n"
+			"movzbl	(%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
+			"addl	$64, %%eax\n\t"
+			"cmpl	%%eax, %[size]\n\t"
+			"jne	.Lfill_cache\n\t"
+			"lfence\n"
+			:: [flush_pages] "r" (l1d_flush_pages),
+			[size] "r" (size)
+			: "eax", "ecx");
+}
+EXPORT_SYMBOL_GPL(l1d_flush_sw);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f35654db904a..4f95927aad4c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6031,8 +6031,6 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
  */
 static void vmx_l1d_flush(struct kvm_vcpu *vcpu)
 {
-	int size = PAGE_SIZE << L1D_CACHE_ORDER;
-
 	/*
 	 * This code is only executed when the the flush mode is 'cond' or
 	 * 'always'
@@ -6061,32 +6059,11 @@ static void vmx_l1d_flush(struct kvm_vcpu *vcpu)
 
 	vcpu->stat.l1d_flush++;
 
-	if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) {
-		wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
+	if (!l1d_flush_hw())
 		return;
-	}
 
-	asm volatile(
-		/* First ensure the pages are in the TLB */
-		"xorl	%%eax, %%eax\n"
-		".Lpopulate_tlb:\n\t"
-		"movzbl	(%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
-		"addl	$4096, %%eax\n\t"
-		"cmpl	%%eax, %[size]\n\t"
-		"jne	.Lpopulate_tlb\n\t"
-		"xorl	%%eax, %%eax\n\t"
-		"cpuid\n\t"
-		/* Now fill the cache */
-		"xorl	%%eax, %%eax\n"
-		".Lfill_cache:\n"
-		"movzbl	(%[flush_pages], %%" _ASM_AX "), %%ecx\n\t"
-		"addl	$64, %%eax\n\t"
-		"cmpl	%%eax, %[size]\n\t"
-		"jne	.Lfill_cache\n\t"
-		"lfence\n"
-		:: [flush_pages] "r" (vmx_l1d_flush_pages),
-		    [size] "r" (size)
-		: "eax", "ebx", "ecx", "edx");
+	l1d_flush_populate_tlb(vmx_l1d_flush_pages);
+	l1d_flush_sw(vmx_l1d_flush_pages);
 }
 
 static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
-- 
2.17.1