Re: [PATCH kvm-unit-tests 3/4] Add support for calling a function in guest mode

Michael S. Tsirkin
2010-11-26T14:18:00Z

On Wed, Nov 24, 2010 at 12:52:12PM +0200, Avi Kivity wrote:
> This patch provides a way to establish an "identity" guest which has
> a 1:1 gva->hva translation. This allows the host to switch to guest
> mode, call a function in the same address space, and return.
>
> Because long mode virtual addresses are 47 bits long, and some hosts
> have smaller physical addresses, we target 32-bit mode only. On
> x86_64 the code needs to be run with 'setarch i386 -3' to limit the
> address space to 3GB, so the address space occupied by the local
> APIC is left unused.
>
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
> api/identity.cc | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
> api/identity.h | 28 ++++++++++++++++++
> config-x86-common.mak | 2 +
> 3 files changed, 106 insertions(+), 0 deletions(-)
> create mode 100644 api/identity.cc
> create mode 100644 api/identity.h
>
> diff --git a/api/identity.cc b/api/identity.cc
> new file mode 100644
> index 0000000..8e86db1
> --- /dev/null
> +++ b/api/identity.cc
> @@ -0,0 +1,76 @@
> +
> +#include "identity.h"
> +#include <stdio.h>
> +
> +namespace identity {
> +
> +typedef unsigned long ulong;
> +
> +void setup_vm(kvm::vm& vm)
> +{
> + vm.set_memory_region(0, NULL, 0, 3UL << 30);
> + vm.set_tss_addr(3UL << 30);
> +}
> +
> +void vcpu::setup_sregs()
> +{
> + kvm_sregs sregs = { };
> + kvm_segment dseg = { };
> + dseg.base = 0; dseg.limit = -1U; dseg.type = 3; dseg.present = 1;
> + dseg.dpl = 3; dseg.db = 1; dseg.s = 1; dseg.l = 0; dseg.g = 1;
> + kvm_segment cseg = dseg;
> + cseg.type = 11;
> +
> + sregs.cs = cseg; asm ("mov %%cs, %0" : "=rm"(sregs.cs.selector));
> + sregs.ds = dseg; asm ("mov %%ds, %0" : "=rm"(sregs.ds.selector));
> + sregs.es = dseg; asm ("mov %%es, %0" : "=rm"(sregs.es.selector));
> + sregs.fs = dseg; asm ("mov %%fs, %0" : "=rm"(sregs.fs.selector));
> + sregs.gs = dseg; asm ("mov %%gs, %0" : "=rm"(sregs.gs.selector));
> + sregs.ss = dseg; asm ("mov %%ss, %0" : "=rm"(sregs.ss.selector));
> +
> + uint32_t gsbase;
> + asm ("mov %%gs:0, %0" : "=r"(gsbase));
> + sregs.gs.base = gsbase;
> +
> + sregs.tr.base = reinterpret_cast<ulong>(&*_stack.begin());
> + sregs.tr.type = 11;
> + sregs.tr.s = 0;
> + sregs.tr.present = 1;
> +
> + sregs.cr0 = 0x11; /* PE, ET, !PG */
> + sregs.cr4 = 0;
> + sregs.efer = 0;
> + sregs.apic_base = 0xfee00000;
> + _vcpu.set_sregs(sregs);
> +}
> +
> +void vcpu::thunk(vcpu* zis)
> +{
> + zis->_guest_func();
> + asm volatile("outb %%al, %%dx" : : "a"(0), "d"(0));
> +}
> +
> +void vcpu::setup_regs()
> +{
> + kvm_regs regs = {};
> + regs.rflags = 0x3202;
> + regs.rsp = reinterpret_cast<ulong>(&*_stack.end());
> + regs.rsp &= ~15UL;
> + ulong* sp = reinterpret_cast<ulong *>(regs.rsp);
> + *--sp = reinterpret_cast<ulong>((char*)this);
> + *--sp = 0;
> + regs.rsp = reinterpret_cast<ulong>(sp);
> + regs.rip = reinterpret_cast<ulong>(&vcpu::thunk);
> + printf("rip %llx\n", regs.rip);
> + _vcpu.set_regs(regs);
> +}
> +
> +vcpu::vcpu(kvm::vcpu& vcpu, boost::function<void ()> guest_func,
> + unsigned long stack_size)
> + : _vcpu(vcpu), _guest_func(guest_func), _stack(stack_size)
> +{
> + setup_sregs();
> + setup_regs();
> +}
> +
> +}
> diff --git a/api/identity.h b/api/identity.h
> new file mode 100644
> index 0000000..025177a
> --- /dev/null
> +++ b/api/identity.h
> @@ -0,0 +1,28 @@
> +#ifndef API_IDENTITY_H
> +#define API_IDENTITY_H
> +
> +#include "kvmxx.h"
> +#include <boost/function.hpp>

This seems to use boost, which is not part of the standard library.
Do we want this dependency?
We'd need a configure check to verify it's installed.

> +#include <vector>
> +
> +namespace identity {
> +
> +void setup_vm(kvm::vm& vm);
> +
> +class vcpu {
> +public:
> + vcpu(kvm::vcpu& vcpu, boost::function<void ()> guest_func,
> + unsigned long stack_size = 256 * 1024);

So the thread stack is moved to use the heap instead?
Can we use pthread_attr_getstacksize and use the regular thread stack?
Good for portability.

> +private:
> + static void thunk(vcpu* vcpu);
> + void setup_regs();
> + void setup_sregs();
> +private:
> + kvm::vcpu& _vcpu;
> + boost::function<void ()> _guest_func;
> + std::vector<char> _stack;
> +};
> +
> +}
> +
> +#endif
> diff --git a/config-x86-common.mak b/config-x86-common.mak
> index b541c1c..0f3387b 100644
> --- a/config-x86-common.mak
> +++ b/config-x86-common.mak
> @@ -79,3 +79,5 @@ arch_clean:
> $(TEST_DIR)/.*.d $(TEST_DIR)/lib/.*.d $(TEST_DIR)/lib/*.o
>
> -include $(TEST_DIR)/.*.d lib/.*.d lib/x86/.*.d
> +
> +api/%.o: CFLAGS += -m32
> \ No newline at end of file
> --
> 1.7.1
>
> --
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