Commit 3fa045be authored Jul 02, 2018 by Paolo Bonzini Committed by Thomas Gleixner Jul 04, 2018

x86/KVM/VMX: Add L1D MSR based flush

336996-Speculative-Execution-Side-Channel-Mitigations.pdf defines a new MSR
(IA32_FLUSH_CMD aka 0x10B) which has similar write-only semantics to other
MSRs defined in the document.

The semantics of this MSR is to allow "finer granularity invalidation of
caching structures than existing mechanisms like WBINVD. It will writeback
and invalidate the L1 data cache, including all cachelines brought in by
preceding instructions, without invalidating all caches (eg. L2 or
LLC). Some processors may also invalidate the first level level instruction
cache on a L1D_FLUSH command. The L1 data and instruction caches may be
shared across the logical processors of a core."

Use it instead of the loop based L1 flush algorithm.

A copy of this document is available at
   https://bugzilla.kernel.org/show_bug.cgi?id=199511



[ tglx: Avoid allocating pages when the MSR is available ]

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent a47dd5f0

arch/x86/include/asm/msr-index.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -76,6 +76,12 @@
		* control required.
		*/

		#define MSR_IA32_FLUSH_CMD 0x0000010b
		#define L1D_FLUSH (1 << 0) /*
		* Writeback and invalidate the
		* L1 data cache.
		*/

		#define MSR_IA32_BBL_CR_CTL 0x00000119
		#define MSR_IA32_BBL_CR_CTL3 0x0000011e

arch/x86/kvm/vmx.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -9580,6 +9580,11 @@ static void __maybe_unused vmx_l1d_flush(void)
		{
		int size = PAGE_SIZE << L1D_CACHE_ORDER;

		if (static_cpu_has(X86_FEATURE_FLUSH_L1D)) {
		wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
		return;
		}

		asm volatile(
		/* First ensure the pages are in the TLB */
		"xorl %%eax, %%eax\n"
		@@ -13158,11 +13163,13 @@ static int __init vmx_setup_l1d_flush(void)
		!boot_cpu_has_bug(X86_BUG_L1TF))
		return 0;

		if (!boot_cpu_has(X86_FEATURE_FLUSH_L1D)) {
		page = alloc_pages(GFP_KERNEL, L1D_CACHE_ORDER);
		if (!page)
		return -ENOMEM;

		vmx_l1d_flush_pages = page_address(page);
		}

		static_branch_enable(&vmx_l1d_should_flush);
		return 0;
		}

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