Re: [PATCH v4 1/6] arch/x86/kvm: Refactor l1d flush lifecycle management

[Tom Lendacky]

On 4/23/20 9:01 AM, Balbir Singh wrote:
> Split out the allocation and free routines to be used in a follow
> up set of patches (to reuse for L1D flushing).
>
> Signed-off-by: Balbir Singh <sblbir@xxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>   arch/x86/include/asm/cacheflush.h |  3 +++
>   arch/x86/kernel/Makefile          |  1 +
>   arch/x86/kernel/l1d_flush.c       | 36 +++++++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/vmx.c            | 25 +++------------------
>   4 files changed, 43 insertions(+), 22 deletions(-)
>   create mode 100644 arch/x86/kernel/l1d_flush.c
>
> diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
> index 63feaf2a5f93..bac56fcd9790 100644
> --- a/arch/x86/include/asm/cacheflush.h
> +++ b/arch/x86/include/asm/cacheflush.h
> @@ -6,6 +6,9 @@
>   #include <asm-generic/cacheflush.h>
>   #include <asm/special_insns.h>
>   
> +#define L1D_CACHE_ORDER 4

Since this is becoming a generic function now, shouldn't this value be 
based on the actual L1D cache size? Is this value based on a 32KB data 
cache and the idea is to write twice the size of the cache to be sure that 
every entry has been replaced - with the second 32KB to catch the odd line 
that might not have been pulled in?

Thanks,
Tom

>   void clflush_cache_range(void *addr, unsigned int size);
> +void *l1d_flush_alloc_pages(void);
> +void l1d_flush_cleanup_pages(void *l1d_flush_pages);
>   
>   #endif /* _ASM_X86_CACHEFLUSH_H */
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 92e1261ec4ec..42c11ca85f1c 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -158,3 +158,4 @@ ifeq ($(CONFIG_X86_64),y)
>   endif
>   
>   obj-$(CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT)	+= ima_arch.o
> +obj-y						+= l1d_flush.o
> diff --git a/arch/x86/kernel/l1d_flush.c b/arch/x86/kernel/l1d_flush.c
> new file mode 100644
> index 000000000000..d605878c8f28
> --- /dev/null
> +++ b/arch/x86/kernel/l1d_flush.c
> @@ -0,0 +1,36 @@
> +#include <linux/mm.h>
> +#include <asm/cacheflush.h>
> +
> +void *l1d_flush_alloc_pages(void)
> +{
> +	struct page *page;
> +	void *l1d_flush_pages = NULL;
> +	int i;
> +
> +	/*
> +	 * This allocation for l1d_flush_pages is not tied to a VM/task's
> +	 * lifetime and so should not be charged to a memcg.
> +	 */
> +	page = alloc_pages(GFP_KERNEL, L1D_CACHE_ORDER);
> +	if (!page)
> +		return NULL;
> +	l1d_flush_pages = page_address(page);
> +
> +	/*
> +	 * Initialize each page with a different pattern in
> +	 * order to protect against KSM in the nested
> +	 * virtualization case.
> +	 */
> +	for (i = 0; i < 1u << L1D_CACHE_ORDER; ++i) {
> +		memset(l1d_flush_pages + i * PAGE_SIZE, i + 1,
> +				PAGE_SIZE);
> +	}
> +	return l1d_flush_pages;
> +}
> +EXPORT_SYMBOL_GPL(l1d_flush_alloc_pages);
> +
> +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);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 83050977490c..225aa8219bac 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -203,14 +203,10 @@ static const struct {
>   	[VMENTER_L1D_FLUSH_NOT_REQUIRED] = {"not required", false},
>   };
>   
> -#define L1D_CACHE_ORDER 4
>   static void *vmx_l1d_flush_pages;
>   
>   static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
>   {
> -	struct page *page;
> -	unsigned int i;
> -
>   	if (!boot_cpu_has_bug(X86_BUG_L1TF)) {
>   		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
>   		return 0;
> @@ -253,24 +249,9 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
>   
>   	if (l1tf != VMENTER_L1D_FLUSH_NEVER && !vmx_l1d_flush_pages &&
>   	    !boot_cpu_has(X86_FEATURE_FLUSH_L1D)) {
> -		/*
> -		 * This allocation for vmx_l1d_flush_pages is not tied to a VM
> -		 * lifetime and so should not be charged to a memcg.
> -		 */
> -		page = alloc_pages(GFP_KERNEL, L1D_CACHE_ORDER);
> -		if (!page)
> +		vmx_l1d_flush_pages = l1d_flush_alloc_pages();
> +		if (!vmx_l1d_flush_pages)
>   			return -ENOMEM;
> -		vmx_l1d_flush_pages = page_address(page);
> -
> -		/*
> -		 * Initialize each page with a different pattern in
> -		 * order to protect against KSM in the nested
> -		 * virtualization case.
> -		 */
> -		for (i = 0; i < 1u << L1D_CACHE_ORDER; ++i) {
> -			memset(vmx_l1d_flush_pages + i * PAGE_SIZE, i + 1,
> -			       PAGE_SIZE);
> -		}
>   	}
>   
>   	l1tf_vmx_mitigation = l1tf;
> @@ -8026,7 +8007,7 @@ static struct kvm_x86_init_ops vmx_init_ops __initdata = {
>   static void vmx_cleanup_l1d_flush(void)
>   {
>   	if (vmx_l1d_flush_pages) {
> -		free_pages((unsigned long)vmx_l1d_flush_pages, L1D_CACHE_ORDER);
> +		l1d_flush_cleanup_pages(vmx_l1d_flush_pages);
>   		vmx_l1d_flush_pages = NULL;
>   	}
>   	/* Restore state so sysfs ignores VMX */