[PATCH] arm64: kvm: Fix kvm teardown for systems using the extended idmap
Christoffer Dall
christoffer.dall at linaro.org
Tue May 3 01:36:51 PDT 2016
On Mon, May 02, 2016 at 01:05:35PM +0100, Marc Zyngier wrote:
> On Fri, 29 Apr 2016 18:27:03 +0100
> James Morse <james.morse at arm.com> wrote:
>
> Hi James,
>
> > If memory is located above 1<<VA_BITS, kvm adds an extra level to its page
> > tables, merging the runtime tables and boot tables that contain the idmap.
> > This lets us avoid the trampoline dance during initialisation.
> >
> > This also means there is no trampoline page mapped, so
> > __cpu_reset_hyp_mode() can't call __kvm_hyp_reset() in this page. The good
> > news is the idmap is still mapped, so we don't need the trampoline page.
> > The bad news is we can't call it directly as the idmap is above
> > HYP_PAGE_OFFSET, so its address is masked by kvm_call_hyp.
> >
> > Add a function __extended_idmap_trampoline which will branch into
> > __kvm_hyp_reset in the idmap, change kvm_hyp_reset_entry() to return
> > this address if __kvm_cpu_uses_extended_idmap(). In this case
> > __kvm_hyp_reset() will still switch to the boot tables (which are the
> > merged tables that were already in use), and branch into the idmap (where
> > it already was).
> >
> > This fixes boot failures on these systems, where we fail to execute the
> > missing trampoline page when tearing down kvm in init_subsystems():
> > [ 2.508922] kvm [1]: 8-bit VMID
> > [ 2.512057] kvm [1]: Hyp mode initialized successfully
> > [ 2.517242] kvm [1]: interrupt-controller at e1140000 IRQ13
> > [ 2.522622] kvm [1]: timer IRQ3
> > [ 2.525783] Kernel panic - not syncing: HYP panic:
> > [ 2.525783] PS:200003c9 PC:0000007ffffff820 ESR:86000005
> > [ 2.525783] FAR:0000007ffffff820 HPFAR:00000000003ffff0 PAR:0000000000000000
> > [ 2.525783] VCPU: (null)
> > [ 2.525783]
> > [ 2.547667] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 4.6.0-rc5+ #1
> > [ 2.555137] Hardware name: Default string Default string/Default string, BIOS ROD0084E 09/03/2015
> > [ 2.563994] Call trace:
> > [ 2.566432] [<ffffff80080888d0>] dump_backtrace+0x0/0x240
> > [ 2.571818] [<ffffff8008088b24>] show_stack+0x14/0x20
> > [ 2.576858] [<ffffff80083423ac>] dump_stack+0x94/0xb8
> > [ 2.581899] [<ffffff8008152130>] panic+0x10c/0x250
> > [ 2.586677] [<ffffff8008152024>] panic+0x0/0x250
> > [ 2.591281] SMP: stopping secondary CPUs
> > [ 3.649692] SMP: failed to stop secondary CPUs 0-2,4-7
> > [ 3.654818] Kernel Offset: disabled
> > [ 3.658293] Memory Limit: none
> > [ 3.661337] ---[ end Kernel panic - not syncing: HYP panic:
> > [ 3.661337] PS:200003c9 PC:0000007ffffff820 ESR:86000005
> > [ 3.661337] FAR:0000007ffffff820 HPFAR:00000000003ffff0 PAR:0000000000000000
> > [ 3.661337] VCPU: (null)
> > [ 3.661337]
> >
> >
> > Reported-by: Will Deacon <will.deacon at arm.com>
> > Signed-off-by: James Morse <james.morse at arm.com>
> > ---
> > arch/arm64/include/asm/kvm_host.h | 3 ++-
> > arch/arm64/kvm/hyp-init.S | 5 +++++
> > arch/arm64/kvm/hyp/entry.S | 19 +++++++++++++++++++
> > arch/arm64/kvm/reset.c | 30 +++++++++++++++++++++++-------
> > 4 files changed, 49 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index b6f194d9f6b2..88a34670ddef 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -46,7 +46,8 @@
> > int __attribute_const__ kvm_target_cpu(void);
> > int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
> > int kvm_arch_dev_ioctl_check_extension(long ext);
> > -phys_addr_t kvm_hyp_reset_entry(void);
> > +unsigned long kvm_hyp_reset_entry(void);
> > +void __extended_idmap_trampoline(phys_addr_t boot_pgd, phys_addr_t idmap_start);
> >
> > struct kvm_arch {
> > /* The VMID generation used for the virt. memory system */
> > diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> > index 44ec4cb23ae7..a873a6d8be90 100644
> > --- a/arch/arm64/kvm/hyp-init.S
> > +++ b/arch/arm64/kvm/hyp-init.S
> > @@ -140,6 +140,11 @@ merged:
> > ENDPROC(__kvm_hyp_init)
> >
> > /*
> > + * Reset kvm back to the hyp stub. This is the trampoline dance in
> > + * reverse. If kvm used an extended idmap, __extended_idmap_trampoline
> > + * calls this code directly in the idmap. In this case switching to the
> > + * boot tables is a no-op.
> > + *
> > * x0: HYP boot pgd
> > * x1: HYP phys_idmap_start
> > */
> > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
> > index ce9e5e5f28cf..70254a65bd5b 100644
> > --- a/arch/arm64/kvm/hyp/entry.S
> > +++ b/arch/arm64/kvm/hyp/entry.S
> > @@ -164,3 +164,22 @@ alternative_endif
> >
> > eret
> > ENDPROC(__fpsimd_guest_restore)
> > +
> > +/*
> > + * When using the extended idmap, we don't have a trampoline page we can use
> > + * while we switch pages tables during __kvm_hyp_reset. Accessing the idmap
> > + * directly would be ideal, but if we're using the extended idmap then the
> > + * idmap is located above HYP_PAGE_OFFSET, and the address will be masked by
> > + * kvm_call_hyp using kern_hyp_va.
> > + *
> > + * x0: HYP boot pgd
> > + * x1: HYP phys_idmap_start
> > + */
> > +ENTRY(__extended_idmap_trampoline)
> > + mov x4, x1
> > + adr_l x3, __kvm_hyp_reset
> > +
> > + /* insert __kvm_hyp_reset()s offset into phys_idmap_start */
> > + bfi x4, x3, #0, #PAGE_SHIFT
> > + br x4
> > +ENDPROC(__extended_idmap_trampoline)
> > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> > index 4062e6dd4cc1..b1ad730e1567 100644
> > --- a/arch/arm64/kvm/reset.c
> > +++ b/arch/arm64/kvm/reset.c
> > @@ -135,12 +135,28 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> >
> > extern char __hyp_idmap_text_start[];
> >
> > -phys_addr_t kvm_hyp_reset_entry(void)
> > +unsigned long kvm_hyp_reset_entry(void)
> > {
> > - unsigned long offset;
> > -
> > - offset = (unsigned long)__kvm_hyp_reset
> > - - ((unsigned long)__hyp_idmap_text_start & PAGE_MASK);
> > -
> > - return TRAMPOLINE_VA + offset;
> > + if (!__kvm_cpu_uses_extended_idmap()) {
> > + unsigned long offset;
> > +
> > + /*
> > + * Find the address of __kvm_hyp_reset() in the trampoline page.
> > + * This is present in the running page tables, and the boot page
> > + * tables, so we call the code here to start the trampoline
> > + * dance in reverse.
> > + */
> > + offset = (unsigned long)__kvm_hyp_reset
> > + - ((unsigned long)__hyp_idmap_text_start & PAGE_MASK);
> > +
> > + return TRAMPOLINE_VA + offset;
> > + } else {
> > + /*
> > + * KVM is running with merged page tables, which don't have the
> > + * trampoline page mapped. We know the idmap is still mapped,
> > + * but can't be called into directly. Use
> > + * __extended_idmap_trampoline to do the call.
> > + */
> > + return (unsigned long)kvm_ksym_ref(__extended_idmap_trampoline);
> > + }
> > }
>
> This looks correct, and gives me yet another incentive to revisit this
> code with a view of keeping the idmap at all times in the EL2 page
> tables. This should ensure that (1) the merged page tables become the
> only configuration, and (2) that we get rid off of the potential TLB
> conflict when swapping TTBR0_EL2 at boot time (intermediate level
> caching). In the meantime:
>
> Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
>
thanks! Will, should this go via the kvmarm tree or the arm64 tree?
-Christoffer
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