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hw: eager FPU switching for x86_64

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Since gcc 8.3.0 generates SSE instructions into kernel code, the
kernel itself may raise FPU exceptions and/or corrupt user level FPU
contexts thereby. Both things are not feasible, and therefore, lazy FPU
switching becomes a no go for base-hw because we cannot avoid FPU
instructions because of the entanglement of base-hw, base, and the tool
chain (libgcc_eh.a).

issue #3365
This commit is contained in:
Sebastian Sumpf 2019-05-23 18:09:42 +02:00 committed by Christian Helmuth
parent 34a711b439
commit da17f2cbd3
11 changed files with 49 additions and 203 deletions
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1
repos/base-hw/lib/mk/spec/x86_64/core-hw-muen.mk
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@ -25,7 +25,6 @@ SRC_CC += spec/x86/io_port_session_component.cc
SRC_CC += spec/x86/io_port_session_support.cc
SRC_CC += spec/x86_64/bios_data_area.cc
SRC_CC += spec/x86_64/cpu.cc
SRC_CC += spec/x86_64/fpu.cc
SRC_CC += spec/x86_64/kernel/cpu.cc
SRC_CC += spec/x86_64/kernel/pd.cc
SRC_CC += spec/x86_64/kernel/thread.cc

1
repos/base-hw/lib/mk/spec/x86_64/core-hw-pc.mk
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@ -26,7 +26,6 @@ SRC_CC += spec/x86/io_port_session_component.cc
SRC_CC += spec/x86/io_port_session_support.cc
SRC_CC += spec/x86_64/bios_data_area.cc
SRC_CC += spec/x86_64/cpu.cc
SRC_CC += spec/x86_64/fpu.cc
SRC_CC += spec/x86_64/kernel/cpu.cc
SRC_CC += spec/x86_64/kernel/pd.cc
SRC_CC += spec/x86_64/kernel/thread.cc

2
repos/base-hw/src/core/spec/x86_64/cpu.cc
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@ -111,8 +111,6 @@ extern Genode::size_t const kernel_stack_size;
void Genode::Cpu::switch_to(Context & context, Mmu_context &mmu_context)
{
_fpu.switch_to(context);
if ((context.cs != 0x8) && (mmu_context.cr3 != Cr3::read()))
Cr3::write(mmu_context.cr3);

7
repos/base-hw/src/core/spec/x86_64/cpu.h
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@ -43,8 +43,6 @@ class Genode::Cpu : public Hw::X86_64_cpu
{
protected:
Fpu _fpu { };
public:
/**
@ -95,7 +93,7 @@ class Genode::Cpu : public Hw::X86_64_cpu
struct Kernel_stack { unsigned long kernel_stack { }; };
/* exception_vector.s depends on the position of the Kernel_stack */
struct alignas(16) Context : Cpu_state, Kernel_stack, Fpu::Context
struct alignas(16) Context : Cpu_state, Kernel_stack, Fpu_context
{
enum Eflags {
EFLAGS_IF_SET = 1 << 9,
@ -113,9 +111,6 @@ class Genode::Cpu : public Hw::X86_64_cpu
Mmu_context(addr_t page_table_base);
};
Fpu & fpu() { return _fpu; }
/**
* Return kernel name of the executing CPU
*/

7
repos/base-hw/src/core/spec/x86_64/exception_vector.s
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@ -119,8 +119,15 @@
.set REGISTER_SIZE, 8
.set SIZEOF_CPU_STATE, REGISTER_COUNT * REGISTER_SIZE /* sizeof (Cpu_state) */
.set KERNEL_STACK_OFFSET, SIZEOF_CPU_STATE
.set FPU_CONTEXT_OFFSET, KERNEL_STACK_OFFSET + 8
/* rsp contains pointer to Cpu::Context */
/* save FPU context */
movq %rsp, %rax
addq $FPU_CONTEXT_OFFSET, %rax
movq (%rax), %rax
fxsave (%rax)
/* Restore kernel stack and continue kernel execution */
movq %rsp, %rax
addq $KERNEL_STACK_OFFSET, %rax

61
repos/base-hw/src/core/spec/x86_64/fpu.cc
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@ -1,61 +0,0 @@
/*
* \brief FPU implementation specific to x86_64
* \author Stefan Kalkowski
* \date 2016-01-19
*/
/*
* Copyright (C) 2016-2017 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
/* core includes */
#include <cpu.h>
void Genode::Fpu::init()
{
Cpu::Cr0::access_t cr0_value = Cpu::Cr0::read();
Cpu::Cr4::access_t cr4_value = Cpu::Cr4::read();
Cpu::Cr0::Mp::set(cr0_value);
Cpu::Cr0::Em::clear(cr0_value);
/*
* Clear task switched so we do not gnerate FPU faults during kernel
* initialisation, it will be turned on by Fpu::disable
*/
Cpu::Cr0::Ts::clear(cr0_value);
Cpu::Cr0::Ne::set(cr0_value);
Cpu::Cr0::write(cr0_value);
Cpu::Cr4::Osfxsr::set(cr4_value);
Cpu::Cr4::Osxmmexcpt::set(cr4_value);
Cpu::Cr4::write(cr4_value);
}
void Genode::Fpu::disable() {
Cpu::Cr0::write(Cpu::Cr0::read() | Cpu::Cr0::Ts::bits(1)); }
bool Genode::Fpu::enabled() { return !Cpu::Cr0::Ts::get(Cpu::Cr0::read()); }
bool Genode::Fpu::fault(Context &context)
{
if (enabled()) return false;
enable();
if (_context == &context) return true;
if (_context) {
_save();
_context->_fpu = nullptr;
}
_context = &context;
_context->_fpu = this;
_load();
return true;
}

155
repos/base-hw/src/core/spec/x86_64/fpu.h
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@ -1,14 +1,11 @@
/*
* \brief x86_64 FPU driver for core
* \author Adrian-Ken Rueegsegger
* \author Martin stein
* \author Reto Buerki
* \author Stefan Kalkowski
* \date 2016-01-19
* \brief x86_64 FPU context
* \author Sebastian Sumpf
* \date 2019-05-23
*/
/*
* Copyright (C) 2016-2017 Genode Labs GmbH
* Copyright (C) 2019 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
@ -18,128 +15,50 @@
#define _CORE__SPEC__X86_64__FPU_H_
/* Genode includes */
#include <base/stdint.h>
#include <util/misc_math.h>
#include <util/mmio.h>
#include <util/string.h>
namespace Genode { class Fpu; }
namespace Genode { class Fpu_context; }
class Genode::Fpu
class Genode::Fpu_context
{
public:
addr_t _fxsave_addr { 0 };
class Context
/*
* FXSAVE area providing storage for x87 FPU, MMX, XMM,
* and MXCSR registers.
*
* For further details see Intel SDM Vol. 2A,
* 'FXSAVE instruction'.
*/
char _fxsave_area[527];
struct Context : Mmio
{
struct Fcw : Register<0, 16> { };
struct Mxcsr : Register<24, 32> { };
Context(addr_t const base) : Mmio(base)
{
private:
friend class Fpu;
/*
* FXSAVE area providing storage for x87 FPU, MMX, XMM,
* and MXCSR registers.
*
* For further details see Intel SDM Vol. 2A,
* 'FXSAVE instruction'.
*/
char _fxsave_area[527];
/* 16-byte aligned start of FXSAVE area. */
char * _start = nullptr;
Fpu * _fpu = nullptr;
bool _init()
{
if (_start) return true;
_start = ((addr_t)_fxsave_area & 15)
? (char *)((addr_t)_fxsave_area & ~15) + 16
: _fxsave_area;
return false;
}
public:
~Context() { if (_fpu) _fpu->unset(*this); }
};
private:
enum { MXCSR_DEFAULT = 0x1f80 };
Context * _context = nullptr;
/**
* Reset FPU
*
* Doesn't check for pending unmasked floating-point
* exceptions and explicitly sets the MXCSR to the
* default value.
*/
void _reset()
{
unsigned value = MXCSR_DEFAULT;
asm volatile ("fninit");
asm volatile ("ldmxcsr %0" : : "m" (value));
memset((void *)base, 0, 512);
write<Fcw>(0x37f); /* mask exceptions SysV ABI */
write<Mxcsr>(0x1f80);
}
/**
* Load x87 FPU context
*/
void _load()
{
if (!_context->_init()) _reset();
else asm volatile ("fxrstor %0" : : "m" (*_context->_start));
}
/**
* Save x87 FPU context
*/
void _save() {
asm volatile ("fxsave %0" : "=m" (*_context->_start)); }
};
public:
/**
* Disable FPU by setting the TS flag in CR0.
*/
void disable();
Fpu_context()
{
/* align to 16 byte boundary */
_fxsave_addr = align_addr((addr_t)_fxsave_area, 4);
/**
* Enable FPU by clearing the TS flag in CR0.
*/
void enable() { asm volatile ("clts"); }
/* set fcw/mxcsr */
Context init(_fxsave_addr);
}
/**
* Initialize all FPU-related CR flags
*
* Initialize FPU with SSE extensions by setting required CR0 and CR4
* bits to configure the FPU environment according to Intel SDM Vol.
* 3A, sections 9.2 and 9.6.
*/
void init();
/**
* Returns True if the FPU is enabled.
*/
bool enabled();
/**
* Switch to new context
*
* \param context next FPU context
*/
void switch_to(Context &context) {
if (_context != &context) disable(); }
/**
* Return whether to retry an FPU instruction after this call
*/
bool fault(Context &context);
/**
* Unset FPU context
*/
void unset(Context &context) {
if (_context == &context) _context = nullptr; }
addr_t fpu_context() const { return _fxsave_addr; }
};
#endif /* _CORE__SPEC__X86_64__FPU_H_ */

2
repos/base-hw/src/core/spec/x86_64/kernel/cpu.cc
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@ -24,8 +24,6 @@ void Kernel::Cpu::_arch_init()
Timer::init_cpu_local();
fpu().init();
/* enable timer interrupt */
_pic.store_apic_id(id());
_pic.unmask(_timer.interrupt_id(), id());

6
repos/base-hw/src/core/spec/x86_64/kernel/thread.cc
View File

@ -41,7 +41,8 @@ void Kernel::Thread::proceed(Cpu & cpu)
{
cpu.switch_to(*regs, pd().mmu_regs);
asm volatile("mov %0, %%rsp \n"
asm volatile("fxrstor (%1) \n"
"mov %0, %%rsp \n"
"popq %%r8 \n"
"popq %%r9 \n"
"popq %%r10 \n"
@ -58,7 +59,8 @@ void Kernel::Thread::proceed(Cpu & cpu)
"popq %%rsi \n"
"popq %%rbp \n"
"add $16, %%rsp \n"
"iretq \n" :: "r" (&regs->r8));
"iretq \n"
:: "r" (&regs->r8), "r" (regs->fpu_context()));
}

5
repos/base-hw/src/core/spec/x86_64/kernel/thread_exception.cc
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@ -27,11 +27,6 @@ void Thread::exception(Cpu & cpu)
case Cpu_state::PAGE_FAULT:
_mmu_exception();
return;
case Cpu_state::NO_MATH_COPROC:
if (_cpu->fpu().fault(*regs)) { return; }
Genode::raw(*this, ": FPU error");
_die();
return;
case Cpu_state::UNDEFINED_INSTRUCTION:
Genode::raw(*this, ": undefined instruction at ip=", (void*)regs->ip);
_die();

5
repos/base-hw/src/core/spec/x86_64/muen/kernel/thread_exception.cc
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@ -25,11 +25,6 @@ void Thread::exception(Cpu & cpu)
case Cpu::Context::PAGE_FAULT:
_mmu_exception();
return;
case Cpu::Context::NO_MATH_COPROC:
if (_cpu->fpu().fault(*regs)) { return; }
Genode::raw(*this, ": FPU error");
_die();
return;
case Cpu::Context::UNDEFINED_INSTRUCTION:
Genode::raw(*this, ": undefined instruction at ip=", (void*)regs->ip);
_die();