A vcpu can pin up to four mmu shadow pages, which means the freeing
loop will never terminate. Fix by first unpinning shadow pages on
all vcpus, then freeing shadow pages.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Switch guest paging context may require us to allocate memory, which
might fail. Instead of wiring up error paths everywhere, make context
switching lazy and actually do the switch before the next guest entry,
where we can return an error if allocation fails.
Signed-off-by: Avi Kivity <avi@qumranet.com>
This was once used to avoid accessing the guest pte when upgrading
the shadow pte from read-only to read-write. But usually we need
to set the guest pte dirty or accessed bits anyway, so this wasn't
really exploited.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Always set the accessed and dirty bit (since having them cleared causes
a read-modify-write cycle), always set the present bit, and copy the
nx bit from the guest.
Signed-off-by: Avi Kivity <avi@qumranet.com>
With guest smp, a second vcpu might see partial updates when the first
vcpu services a page fault. So delay all updates until we have figured
out what the pte should look like.
Note that on i386, this is still not completely atomic as a 64-bit write
will be split into two on a 32-bit machine.
Signed-off-by: Avi Kivity <avi@qumranet.com>
This prevents some work from being performed twice, and, more importantly,
reduces the number of places where we modify shadow ptes.
Signed-off-by: Avi Kivity <avi@qumranet.com>
We will need the accessed bit (in addition to the dirty bit) and
also write access (for setting the dirty bit) in a future patch.
Signed-off-by: Avi Kivity <avi@qumranet.com>
KVM compilation fails for some .configs. This fixes it.
Signed-off-by: Markus Rechberger <markus.rechberger@amd.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Make a "menuconfig" out of the Kconfig objects "menu, ..., endmenu",
so that the user can disable all the options in that menu at once
instead of having to disable each option separately.
Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Avi Kivity <avi@qumranet.com>
MSR_EFER.LME/LMA bits are automatically save/restored by VMX
hardware, KVM only needs to save NX/SCE bits at time of heavy
weight VM Exit. But clearing NX bits in host envirnment may
cause system hang if the host page table is using EXB bits,
thus we leave NX bits as it is. If Host NX=1 and guest NX=0, we
can do guest page table EXB bits check before inserting a shadow
pte (though no guest is expecting to see this kind of gp fault).
If host NX=0, we present guest no Execute-Disable feature to guest,
thus no host NX=0, guest NX=1 combination.
This patch reduces raw vmexit time by ~27%.
Me: fix compile warnings on i386.
Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
In a lightweight exit (where we exit and reenter the guest without
scheduling or exiting to userspace in between), we don't need various
msrs on the host, and avoiding shuffling them around reduces raw exit
time by 8%.
i386 compile fix by Daniel Hecken <dh@bahntechnik.de>.
Signed-off-by: Yaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Instructions with address size override prefix opcode 0x67
Cause the #SS fault with 0 error code in VM86 mode. Forward
them to the emulator.
Signed-Off-By: Nitin A Kamble <nitin.a.kamble@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
kunmap() expects a struct page, not a virtual address. Fixes an oops loading
kvm-intel.ko on i386 with CONFIG_HIGHMEM.
Thanks to Michael Ivanov <deruhu@peterstar.ru> for reporting.
Signed-off-by: Avi Kivity <avi@qumranet.com>
The real mode tr needs to be set to a specific tss so that I/O
instructions can function. Divert the new tr values to the real
mode save area from where they will be restored on transition to
protected mode.
This fixes some crashes on reboot when the bios accesses an I/O
instruction.
Signed-off-by: Avi Kivity <avi@qumranet.com>
If we set an msr via an ioctl() instead of by handling a guest exit, we
have the host state loaded, so reloading the msrs would clobber host
state instead of guest state.
This fixes a host oops (and loss of a cpu) on a guest reboot.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Attempting to boot the default 'bsd' kernel of OpenBSD 4.1 i386 in a guest
fails early in the kernel init inside p3_get_bus_clock while trying to read
the IA32_EBL_CR_POWERON MSR. KVM logs an 'unhandled MSR' message and the
guest kernel faults.
This patch is sufficient to allow OpenBSD to boot, after which it seems to
run fine. I'm not sure if this is the correct solution for dealing with
this particular MSR, but it works for me.
Signed-off-by: Matthew Gregan <kinetik@flim.org>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Everyone owns a piece of the exception bitmap, but they happily write to
the entire thing like there's no tomorrow. Centralize handling in
update_exception_bitmap() and have everyone call that.
Signed-off-by: Avi Kivity <avi@qumranet.com>
The lightweight vmexit path avoids saving and reloading certain host
state. However in certain cases lightweight vmexit handling can schedule()
which requires reloading the host state.
So we store the host state in the vcpu structure, and reloaded it if we
relinquish the vcpu.
Signed-off-by: Avi Kivity <avi@qumranet.com>
A typical demand page/copy on write pattern is:
- page fault on vaddr
- kvm propagates fault to guest
- guest handles fault, updates pte
- kvm traps write, clears shadow pte, resumes guest
- guest returns to userspace, re-faults on same vaddr
- kvm installs shadow pte, resumes guest
- guest continues
So, three vmexits for a single guest page fault. But if instead of clearing
the page table entry, we update to correspond to the value that the guest
has just written, we eliminate the third vmexit.
This patch does exactly that, reducing kbuild time by about 10%.
Signed-off-by: Avi Kivity <avi@qumranet.com>
When a guest writes to a page that has an mmu shadow, we have to clear
the shadow pte corresponding to the memory location touched by the guest.
Now, in nonpae mode, a single guest page may have two or four shadow
pages (because a nonpae page maps 4MB or 4GB, whereas the pae shadow maps
2MB or 1GB), so we when we look up the page we find up to three additional
aliases for the page. Since we _clear_ the shadow pte, it doesn't matter
except for a slight performance penalty, but if we want to _update_ the
shadow pte instead of clearing it, it is vital that we don't modify the
aliases.
Fortunately, exactly which page is needed (the "quadrant") is easily
computed, and is accessible in the shadow page header. All we need is
to ignore shadow pages from the wrong quadrants.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Instead of calling two functions and repeating expensive checks, call one
function and provide it with before/after information.
Signed-off-by: Avi Kivity <avi@qumranet.com>
i386 wants fs for accessing the pda even on a lightweight exit, so ensure
we can always restore it. This fixes a regression on i386 introduced by
the lightweight vmexit patch.
Signed-off-by: Avi Kivity <avi@qumranet.com>
The kvm mmu tries to detects forks by looking for repeated writes to a
page table. If it sees a fork, it unshadows the page table so the page
table copying can proceed at native speed instead of being emulated.
However, the detector also triggered on simple demand paging access patterns:
a linear walk of memory would of course cause repeated writes to the same
pagetable page, causing it to unshadow prematurely.
Fix by resetting the fork detector if we detect a demand fault.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Many msrs and the like will only be used by the host if we schedule() or
return to userspace. Therefore, we avoid saving them if we handle the
exit within the kernel, and if a reschedule is not requested.
Based on a patch from Eddie Dong <eddie.dong@intel.com> with a couple of
fixes by me.
Signed-off-by: Yaozu(Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This allows us to remove write protection earlier than otherwise. Should
some mad OS choose to use byte writes to update pagetables, it will suffer
a performance hit, but still work correctly.
Signed-off-by: Avi Kivity <avi@qumranet.com>
The PC debug port is used for IO delay and does not require emulation.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This patch enables IO bitmaps control on vmx and unmask the 0x80 port to
avoid VMEXITs caused by accessing port 0x80. 0x80 is used as delays (see
include/asm/io.h), and handling VMEXITs on its access is unnecessary but
slows things down. This patch improves kernel build test at around
3%~5%.
Because every VM uses the same io bitmap, it is shared between
all VMs rather than a per-VM data structure.
Signed-off-by: Qing He <qing.he@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
