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SubjectRe: [PATCH v2 1/4] arch/x86/kvm: Refactor l1d flush lifecycle management
On Mon, Apr 06, 2020 at 01:19:43PM +1000, 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@amazon.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> 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..6419a4cef0e8 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
> void clflush_cache_range(void *addr, unsigned int size);
> +void *alloc_l1d_flush_pages(void);
> +void cleanup_l1d_flush_pages(void *l1d_flush_pages);
>
> #endif /* _ASM_X86_CACHEFLUSH_H */
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index d6d61c4455fa..48f443e6c2de 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -160,3 +160,4 @@ 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..05f375c33423
> --- /dev/null
> +++ b/arch/x86/kernel/l1d_flush.c
> @@ -0,0 +1,36 @@
> +#include <linux/mm.h>
> +#include <asm/cacheflush.h>
> +
> +void *alloc_l1d_flush_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(alloc_l1d_flush_pages);
> +
> +void cleanup_l1d_flush_pages(void *l1d_flush_pages)
> +{
> + free_pages((unsigned long)l1d_flush_pages, L1D_CACHE_ORDER);
> +}
> +EXPORT_SYMBOL_GPL(cleanup_l1d_flush_pages);
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9eaccf92d616..209e63798435 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 = alloc_l1d_flush_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;
> @@ -7992,7 +7973,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
> static void vmx_cleanup_l1d_flush(void)
> {
> if (vmx_l1d_flush_pages) {
> - free_pages((unsigned long)vmx_l1d_flush_pages, L1D_CACHE_ORDER);
> + cleanup_l1d_flush_pages(vmx_l1d_flush_pages);
> vmx_l1d_flush_pages = NULL;
> }
> /* Restore state so sysfs ignores VMX */
> --
> 2.17.1
>

--
Kees Cook

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