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linux/arch/powerpc/kvm/book3s_hv_interrupts.S
Paul Mackerras 8b24e69fc4 KVM: PPC: Book3S HV: Close race with testing for signals on guest entry 
At present, interrupts are hard-disabled fairly late in the guest
entry path, in the assembly code.  Since we check for pending signals
for the vCPU(s) task(s) earlier in the guest entry path, it is
possible for a signal to be delivered before we enter the guest but
not be noticed until after we exit the guest for some other reason.

Similarly, it is possible for the scheduler to request a reschedule
while we are in the guest entry path, and we won't notice until after
we have run the guest, potentially for a whole timeslice.

Furthermore, with a radix guest on POWER9, we can take the interrupt
with the MMU on.  In this case we end up leaving interrupts
hard-disabled after the guest exit, and they are likely to stay
hard-disabled until we exit to userspace or context-switch to
another process.  This was masking the fact that we were also not
setting the RI (recoverable interrupt) bit in the MSR, meaning
that if we had taken an interrupt, it would have crashed the host
kernel with an unrecoverable interrupt message.

To close these races, we need to check for signals and reschedule
requests after hard-disabling interrupts, and then keep interrupts
hard-disabled until we enter the guest.  If there is a signal or a
reschedule request from another CPU, it will send an IPI, which will
cause a guest exit.

This puts the interrupt disabling before we call kvmppc_start_thread()
for all the secondary threads of this core that are going to run vCPUs.
The reason for that is that once we have started the secondary threads
there is no easy way to back out without going through at least part
of the guest entry path.  However, kvmppc_start_thread() includes some
code for radix guests which needs to call smp_call_function(), which
must be called with interrupts enabled.  To solve this problem, this
patch moves that code into a separate function that is called earlier.

When the guest exit is caused by an external interrupt, a hypervisor
doorbell or a hypervisor maintenance interrupt, we now handle these
using the replay facility.  __kvmppc_vcore_entry() now returns the
trap number that caused the exit on this thread, and instead of the
assembly code jumping to the handler entry, we return to C code with
interrupts still hard-disabled and set the irq_happened flag in the
PACA, so that when we do local_irq_enable() the appropriate handler
gets called.

With all this, we now have the interrupt soft-enable flag clear while
we are in the guest.  This is useful because code in the real-mode
hypercall handlers that checks whether interrupts are enabled will
now see that they are disabled, which is correct, since interrupts
are hard-disabled in the real-mode code.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2017-07-01 18:59:38 +10:00

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/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License, version 2, as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* Copyright 2011 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
*
* Derived from book3s_interrupts.S, which is:
* Copyright SUSE Linux Products GmbH 2009
*
* Authors: Alexander Graf <agraf@suse.de>
*/
#include <asm/ppc_asm.h>
#include <asm/kvm_asm.h>
#include <asm/reg.h>
#include <asm/page.h>
#include <asm/asm-offsets.h>
#include <asm/exception-64s.h>
#include <asm/ppc-opcode.h>
/*****************************************************************************
* *
* Guest entry / exit code that is in kernel module memory (vmalloc) *
* *
****************************************************************************/
/* Registers:
* none
*/
_GLOBAL(__kvmppc_vcore_entry)
/* Write correct stack frame */
mflr r0
std r0,PPC_LR_STKOFF(r1)
/* Save host state to the stack */
stdu r1, -SWITCH_FRAME_SIZE(r1)
/* Save non-volatile registers (r14 - r31) and CR */
SAVE_NVGPRS(r1)
mfcr r3
std r3, _CCR(r1)
/* Save host DSCR */
mfspr r3, SPRN_DSCR
std r3, HSTATE_DSCR(r13)
BEGIN_FTR_SECTION
/* Save host DABR */
mfspr r3, SPRN_DABR
std r3, HSTATE_DABR(r13)
END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
/* Save host PMU registers */
BEGIN_FTR_SECTION
/* Work around P8 PMAE bug */
li r3, -1
clrrdi r3, r3, 10
mfspr r8, SPRN_MMCR2
mtspr SPRN_MMCR2, r3 /* freeze all counters using MMCR2 */
isync
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
li r3, 1
sldi r3, r3, 31 /* MMCR0_FC (freeze counters) bit */
mfspr r7, SPRN_MMCR0 /* save MMCR0 */
mtspr SPRN_MMCR0, r3 /* freeze all counters, disable interrupts */
mfspr r6, SPRN_MMCRA
/* Clear MMCRA in order to disable SDAR updates */
li r5, 0
mtspr SPRN_MMCRA, r5
isync
ld r3, PACALPPACAPTR(r13) /* is the host using the PMU? */
lbz r5, LPPACA_PMCINUSE(r3)
cmpwi r5, 0
beq 31f /* skip if not */
mfspr r5, SPRN_MMCR1
mfspr r9, SPRN_SIAR
mfspr r10, SPRN_SDAR
std r7, HSTATE_MMCR0(r13)
std r5, HSTATE_MMCR1(r13)
std r6, HSTATE_MMCRA(r13)
std r9, HSTATE_SIAR(r13)
std r10, HSTATE_SDAR(r13)
BEGIN_FTR_SECTION
mfspr r9, SPRN_SIER
std r8, HSTATE_MMCR2(r13)
std r9, HSTATE_SIER(r13)
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
mfspr r3, SPRN_PMC1
mfspr r5, SPRN_PMC2
mfspr r6, SPRN_PMC3
mfspr r7, SPRN_PMC4
mfspr r8, SPRN_PMC5
mfspr r9, SPRN_PMC6
stw r3, HSTATE_PMC1(r13)
stw r5, HSTATE_PMC2(r13)
stw r6, HSTATE_PMC3(r13)
stw r7, HSTATE_PMC4(r13)
stw r8, HSTATE_PMC5(r13)
stw r9, HSTATE_PMC6(r13)
31:
/*
* Put whatever is in the decrementer into the
* hypervisor decrementer.
*/
BEGIN_FTR_SECTION
ld r5, HSTATE_KVM_VCORE(r13)
ld r6, VCORE_KVM(r5)
ld r9, KVM_HOST_LPCR(r6)
andis. r9, r9, LPCR_LD@h
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
mfspr r8,SPRN_DEC
mftb r7
BEGIN_FTR_SECTION
/* On POWER9, don't sign-extend if host LPCR[LD] bit is set */
bne 32f
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
extsw r8,r8
32: mtspr SPRN_HDEC,r8
add r8,r8,r7
std r8,HSTATE_DECEXP(r13)
/* Jump to partition switch code */
bl kvmppc_hv_entry_trampoline
nop
/*
* We return here in virtual mode after the guest exits
* with something that we can't handle in real mode.
* Interrupts are enabled again at this point.
*/
/*
* Register usage at this point:
*
* R1 = host R1
* R2 = host R2
* R3 = trap number on this thread
* R12 = exit handler id
* R13 = PACA
*/
/* Restore non-volatile host registers (r14 - r31) and CR */
REST_NVGPRS(r1)
ld r4, _CCR(r1)
mtcr r4
addi r1, r1, SWITCH_FRAME_SIZE
ld r0, PPC_LR_STKOFF(r1)
mtlr r0
blr
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