From: Dave Hansen <dave@sr71.net>
To: dave@sr71.net
Cc: dave.hansen@linux.intel.com, mingo@redhat.com, x86@kernel.org,
bp@alien8.de, fenghua.yu@intel.com, tim.c.chen@linux.intel.com,
linux-kernel@vger.kernel.org
Subject: [PATCH 03/15] x86, fpu: remove XSTATE_RESERVE
Date: Wed, 02 Sep 2015 16:31:25 -0700 [thread overview]
Message-ID: <20150902233125.D948D475@viggo.jf.intel.com> (raw)
In-Reply-To: <20150902233123.3A7E5FB0@viggo.jf.intel.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
The original purpose of XSTATE_RESERVE was to carve out space
to store all of the possible extended state components that
get saved with the XSAVE instruction(s).
However, we are now almost entirely dynamically allocating
the buffers we use for XSAVE by placing them at the end of
the task_struct and them sizing them at boot. The one
exception for that is the init_task.
The maximum extended state component size that we have today
is on systems with space for AVX-512 and Memory Protection
Keys: 2696 bytes. We have reserved a PAGE_SIZE buffer in
the init_task via fpregs_state->__padding.
This check ensures that even if the component sizes or
layout were changed (which we do not expect), that we will
still not overflow the init_task's buffer.
In the case that we detect we might overflow the buffer,
we completely disable XSAVE support in the kernel and try
to boot as if we had 'legacy x87 FPU' support in place.
This is a crippled state without any of the XSAVE-enabled
features (MPX, AVX, etc...). But, it at least let us
boot safely.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org
---
b/arch/x86/include/asm/fpu/types.h | 15 ++++-----
b/arch/x86/kernel/fpu/xstate.c | 60 ++++++++++++++++++++++++++++++++-----
2 files changed, 59 insertions(+), 16 deletions(-)
diff -puN arch/x86/include/asm/fpu/types.h~remove-xstate_reserve arch/x86/include/asm/fpu/types.h
--- a/arch/x86/include/asm/fpu/types.h~remove-xstate_reserve 2015-09-02 15:52:48.449823403 -0700
+++ b/arch/x86/include/asm/fpu/types.h 2015-09-02 16:26:23.562389888 -0700
@@ -159,22 +159,19 @@ struct xstate_header {
u64 reserved[6];
} __attribute__((packed));
-/* New processor state extensions should be added here: */
-#define XSTATE_RESERVE (sizeof(struct ymmh_struct) + \
- sizeof(struct lwp_struct) + \
- sizeof(struct mpx_struct) )
/*
* This is our most modern FPU state format, as saved by the XSAVE
* and restored by the XRSTOR instructions.
*
* It consists of a legacy fxregs portion, an xstate header and
- * subsequent fixed size areas as defined by the xstate header.
- * Not all CPUs support all the extensions.
+ * subsequent areas as defined by the xstate header. Not all CPUs
+ * support all the extensions, so the size of the extended area
+ * can vary quite a bit between CPUs.
*/
struct xregs_state {
struct fxregs_state i387;
struct xstate_header header;
- u8 __reserved[XSTATE_RESERVE];
+ u8 extended_state_area[0];
} __attribute__ ((packed, aligned (64)));
/*
@@ -182,7 +179,9 @@ struct xregs_state {
* put together, so that we can pick the right one runtime.
*
* The size of the structure is determined by the largest
- * member - which is the xsave area:
+ * member - which is the xsave area. The padding is there
+ * to ensure that statically-allocated task_structs (just
+ * the init_task today) have enough space.
*/
union fpregs_state {
struct fregs_state fsave;
diff -puN arch/x86/kernel/fpu/xstate.c~remove-xstate_reserve arch/x86/kernel/fpu/xstate.c
--- a/arch/x86/kernel/fpu/xstate.c~remove-xstate_reserve 2015-09-02 15:52:48.451823494 -0700
+++ b/arch/x86/kernel/fpu/xstate.c 2015-09-02 16:26:19.740216279 -0700
@@ -312,24 +312,64 @@ static void __init setup_init_fpu_buf(vo
/*
* Calculate total size of enabled xstates in XCR0/xfeatures_mask.
*/
-static void __init init_xstate_size(void)
+static unsigned int __init calculate_xstate_size(void)
{
unsigned int eax, ebx, ecx, edx;
+ unsigned int calculated_xstate_size;
int i;
if (!cpu_has_xsaves) {
cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
- xstate_size = ebx;
- return;
+ calculated_xstate_size = ebx;
+ return calculated_xstate_size;
}
- xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
+ calculated_xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
for (i = 2; i < 64; i++) {
if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
- xstate_size += eax;
+ calculated_xstate_size += eax;
}
}
+ return calculated_xstate_size;
+}
+
+/*
+ * Will the runtime-enumerated 'xstate_size' fit in the init
+ * task's statically-allocated buffer?
+ */
+static bool is_supported_xstate_size(unsigned int test_xstate_size)
+{
+ if (test_xstate_size <= sizeof(union fpregs_state))
+ return true;
+
+ pr_warn("x86/fpu: xstate buffer too small (%zu < %d), disabling xsave\n",
+ sizeof(union fpregs_state), test_xstate_size);
+ return false;
+}
+
+static int init_xstate_size(void)
+{
+ /* Recompute the context size for enabled features: */
+ unsigned int possible_xstate_size = calculate_xstate_size();
+
+ /* Ensure we have the space to store all enabled: */
+ if (!is_supported_xstate_size(possible_xstate_size))
+ return -EINVAL;
+
+ /*
+ * The size is OK, we are definitely going to use xsave,
+ * make it known to the world that we need more space.
+ */
+ xstate_size = possible_xstate_size;
+ return 0;
+}
+
+void fpu__init_disable_system_xstate(void)
+{
+ xfeatures_mask = 0;
+ cr4_clear_bits(X86_CR4_OSXSAVE);
+ fpu__xstate_clear_all_cpu_caps();
}
/*
@@ -340,6 +380,7 @@ void __init fpu__init_system_xstate(void
{
unsigned int eax, ebx, ecx, edx;
static int on_boot_cpu = 1;
+ int err;
WARN_ON_FPU(!on_boot_cpu);
on_boot_cpu = 0;
@@ -367,9 +408,12 @@ void __init fpu__init_system_xstate(void
/* Enable xstate instructions to be able to continue with initialization: */
fpu__init_cpu_xstate();
-
- /* Recompute the context size for enabled features: */
- init_xstate_size();
+ err = init_xstate_size();
+ if (err) {
+ /* something went wrong, boot without any XSAVE support */
+ fpu__init_disable_system_xstate();
+ return;
+ }
update_regset_xstate_info(xstate_size, xfeatures_mask);
fpu__init_prepare_fx_sw_frame();
_
next prev parent reply other threads:[~2015-09-02 23:35 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-02 23:31 [PATCH 00/15] [v4] x86, fpu: XSAVE cleanups and sanity checks Dave Hansen
2015-09-02 23:31 ` [PATCH 01/15] x86, fpu: print xfeature buffer size in decimal Dave Hansen
2015-09-14 12:19 ` [tip:x86/fpu] x86/fpu: Print " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 02/15] x86, fpu: move XSAVE-disabling code to a helper Dave Hansen
2015-09-14 12:19 ` [tip:x86/fpu] x86/fpu: Move " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 04/15] x86, fpu: kill LWP support Dave Hansen
2015-09-14 12:20 ` [tip:x86/fpu] x86/fpu: Remove partial LWP support definitions tip-bot for Dave Hansen
2015-09-02 23:31 ` Dave Hansen [this message]
2015-09-14 12:20 ` [tip:x86/fpu] x86/fpu: Remove XSTATE_RESERVE tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 05/15] x86, fpu: XSAVE macro renames Dave Hansen
2015-09-14 12:21 ` [tip:x86/fpu] x86/fpu: Rename XSAVE macros tip-bot for Dave Hansen
2015-09-23 10:49 ` Borislav Petkov
2015-09-24 7:24 ` [tip:x86/fpu] x86/fpu: Fixup uninitialized feature_name warning tip-bot for Borislav Petkov
2015-09-02 23:31 ` [PATCH 06/15] x86, fpu: rename XFEATURES_NR_MAX Dave Hansen
2015-09-14 12:21 ` [tip:x86/fpu] x86/fpu: Rename XFEATURES_NR_MAX tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 08/15] x86, fpu: remove xfeature_nr Dave Hansen
2015-09-14 12:22 ` [tip:x86/fpu] x86/fpu: Remove 'xfeature_nr' tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 07/15] x86, fpu: rework XSTATE_* macros to remove magic '2' Dave Hansen
2015-09-14 12:21 ` [tip:x86/fpu] x86/fpu: Rework " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 12/15] x86, fpu: add C structures for AVX-512 state components Dave Hansen
2015-09-14 12:23 ` [tip:x86/fpu] x86/fpu: Add " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 10/15] x86, fpu: rework MPX 'xstate' types Dave Hansen
2015-09-14 12:22 ` [tip:x86/fpu] x86/fpu/mpx: Rework " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 09/15] x86, fpu: add helper xfeature_enabled() instead of test_bit() Dave Hansen
2015-09-14 12:22 ` [tip:x86/fpu] x86/fpu: Add xfeature_enabled() helper " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 11/15] x86, fpu: rework YMM definition Dave Hansen
2015-09-14 12:23 ` [tip:x86/fpu] x86/fpu: Rework " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 14/15] x86, fpu: check to ensure increasing-offset xstate offsets Dave Hansen
2015-09-14 12:24 ` [tip:x86/fpu] x86/fpu: Check " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 13/15] x86, fpu: correct and check XSAVE xstate size calculations Dave Hansen
2015-09-14 12:23 ` [tip:x86/fpu] x86/fpu: Correct " tip-bot for Dave Hansen
2015-09-02 23:31 ` [PATCH 15/15] x86, fpu: check CPU-provided sizes against struct declarations Dave Hansen
2015-09-14 12:24 ` [tip:x86/fpu] x86/fpu: Check " tip-bot for Dave Hansen
2015-09-14 10:07 ` [PATCH 00/15] [v4] x86, fpu: XSAVE cleanups and sanity checks Ingo Molnar
-- strict thread matches above, loose matches on Subject: below --
2015-08-31 22:20 [PATCH 00/15] [v3] " Dave Hansen
2015-08-31 22:20 ` [PATCH 03/15] x86, fpu: remove XSTATE_RESERVE Dave Hansen
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