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Date: Fri, 7 Sep 2018 12:57:30 -0500
From: Brijesh Singh <brijesh.singh@....com>
To: x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: Brijesh Singh <brijesh.singh@....com>,
Tom Lendacky <thomas.lendacky@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH v6 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active
Currently, the per-cpu pvclock data is allocated dynamically when
cpu > HVC_BOOT_ARRAY_SIZE. The physical address of this variable is
shared between the guest and the hypervisor hence it must be mapped as
unencrypted (ie. C=0) when SEV is active.
The C-bit works on a page, hence we will be required to perform a
full 4k page allocation to store a single 32-byte pvclock variable. It
will waste fairly sizeable amount of memory since each CPU will be doing
a separate 4k allocation. Let's define a second array for the SEV case to
statically allocate for NR_CPUS and put this array in .data..decrypted
section so that its mapped with C=0 during boot. The .data..decrypted
section has a big chunk of memory that is currently unused. And since
second array will be used only when memory encryption is active hence
free it when encryption is not active.
Signed-off-by: Brijesh Singh <brijesh.singh@....com>
Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: kvm@...r.kernel.org
Cc: "Radim Krčmář" <rkrcmar@...hat.com>
---
arch/x86/include/asm/mem_encrypt.h | 4 ++++
arch/x86/kernel/kvmclock.c | 14 ++++++++++++++
arch/x86/kernel/vmlinux.lds.S | 3 +++
arch/x86/mm/init.c | 3 +++
arch/x86/mm/mem_encrypt.c | 10 ++++++++++
5 files changed, 34 insertions(+)
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 802b2eb..cc46584 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -48,11 +48,13 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size);
/* Architecture __weak replacement functions */
void __init mem_encrypt_init(void);
+void __init free_decrypted_mem(void);
bool sme_active(void);
bool sev_active(void);
#define __decrypted __attribute__((__section__(".data..decrypted")))
+#define __decrypted_aux __attribute__((__section__(".data..decrypted.aux")))
#else /* !CONFIG_AMD_MEM_ENCRYPT */
@@ -80,6 +82,7 @@ static inline int __init
early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }
#define __decrypted
+#define __decrypted_aux
#endif /* CONFIG_AMD_MEM_ENCRYPT */
@@ -93,6 +96,7 @@ early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0;
#define __sme_pa_nodebug(x) (__pa_nodebug(x) | sme_me_mask)
extern char __start_data_decrypted[], __end_data_decrypted[];
+extern char __start_data_decrypted_aux[];
#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 376fd3a..6086b56 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -65,6 +65,15 @@ static struct pvclock_vsyscall_time_info
static struct pvclock_wall_clock wall_clock __decrypted;
static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+/*
+ * The auxiliary array will be used when SEV is active. In non-SEV case,
+ * it will be freed by free_decrypted_mem().
+ */
+static struct pvclock_vsyscall_time_info
+ hv_clock_aux[NR_CPUS] __decrypted_aux;
+#endif
+
static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
{
return &this_cpu_read(hv_clock_per_cpu)->pvti;
@@ -269,6 +278,11 @@ static int kvmclock_setup_percpu(unsigned int cpu)
/* Use the static page for the first CPUs, allocate otherwise */
if (cpu < HVC_BOOT_ARRAY_SIZE)
p = &hv_clock_boot[cpu];
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ /* Use the static page from auxiliary array instead of allocating it. */
+ else if (sev_active())
+ p = &hv_clock_aux[cpu - HVC_BOOT_ARRAY_SIZE];
+#endif
else
p = kzalloc(sizeof(*p), GFP_KERNEL);
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 4cb1064..bde287a 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -77,6 +77,9 @@ jiffies_64 = jiffies;
. = ALIGN(PMD_SIZE); \
__start_data_decrypted = .; \
*(.data..decrypted); \
+ . = ALIGN(PAGE_SIZE); \
+ __start_data_decrypted_aux = .; \
+ *(.data..decrypted.aux); \
. = ALIGN(PMD_SIZE); \
__end_data_decrypted = .; \
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 7a8fc26..052b279 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -815,9 +815,12 @@ void free_kernel_image_pages(void *begin, void *end)
set_memory_np_noalias(begin_ul, len_pages);
}
+void __weak free_decrypted_mem(void) { }
+
void __ref free_initmem(void)
{
e820__reallocate_tables();
+ free_decrypted_mem();
free_kernel_image_pages(&__init_begin, &__init_end);
}
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index b2de398..9a08c52 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -348,6 +348,16 @@ bool sev_active(void)
EXPORT_SYMBOL(sev_active);
/* Architecture __weak replacement functions */
+void __init free_decrypted_mem(void)
+{
+ if (mem_encrypt_active())
+ return;
+
+ free_init_pages("unused decrypted",
+ (unsigned long)__start_data_decrypted_aux,
+ (unsigned long)__end_data_decrypted);
+}
+
void __init mem_encrypt_init(void)
{
if (!sme_me_mask)
--
2.7.4
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