From: Gleb Natapov <gleb@redhat.com>
To: Sanjay Lal <sanjayl@kymasys.com>
Cc: kvm@vger.kernel.org, linux-mips@linux-mips.org
Subject: Re: [PATCH v2 07/18] KVM/MIPS32: MMU/TLB operations for the Guest.
Date: Fri, 15 Feb 2013 20:41:59 +0200 [thread overview]
Message-ID: <20130215184159.GA16755@redhat.com> (raw)
In-Reply-To: <69F3ED2A-A9B3-4046-9B40-98125ED5A8FB@kymasys.com>
On Fri, Feb 15, 2013 at 01:19:29PM -0500, Sanjay Lal wrote:
>
> On Feb 6, 2013, at 7:08 AM, Gleb Natapov wrote:
>
> >>
> >> +static void kvm_mips_map_page(struct kvm *kvm, gfn_t gfn)
> >> +{
> >> + pfn_t pfn;
> >> +
> >> + if (kvm->arch.guest_pmap[gfn] != KVM_INVALID_PAGE)
> >> + return;
> >> +
> >> + pfn =kvm_mips_gfn_to_pfn(kvm, gfn);
> > This call should be in srcu read section since it access memory slots which
> > are srcu protected. You should test with RCU debug enabled.
>
> kvm_mips_gfn_to_pfn just maps to gfn_to_pfn. I don't see an instance where gfn_to_pfn is in a scru read section?
>
Where are you looking? On x86 if vcpu is not in a guest mode it is in
srcu read section. The lock is taken immediately after exit and released
before entry. This is because x86 access memory slots a lot. Other
arches, that do not access memory slots as much, take the lock around
each individual access. As far as I see this is the only place in MIPS
kvm where this is needed.
> >
> >>
> >> +
> >> +uint32_t kvm_get_inst(uint32_t *opc, struct kvm_vcpu *vcpu)
> >> +{
> >> + uint32_t inst;
> >> + struct mips_coproc *cop0 __unused = vcpu->arch.cop0;
> >> + int index;
> >> + ulong paddr, flags;
> >> +
> >> + if (KVM_GUEST_KSEGX((ulong) opc) < KVM_GUEST_KSEG0 ||
> >> + KVM_GUEST_KSEGX((ulong) opc) == KVM_GUEST_KSEG23) {
> >> + local_irq_save(flags);
> >> + index = kvm_mips_host_tlb_lookup(vcpu, (ulong) opc);
> >> + if (index >= 0) {
> >> + inst = *(opc);
> > Here and in some more places below you access __user memory. Shouldn't you
> > use get_user() to access it? What prevents the kernel crash by access fault here
> > if userspace remaps the memory to be non-readable? Hmm, may be it uses
> > guest translation here so it cannot happen, but still, sparse will not
> > be happy and kvm_mips_translate_guest_kseg0_to_hpa() case below uses
> > host translation anyway.
> >
> Actually, I don't need the __user declaration in most cases, since KVM/MIPS handles mapping the page (if needed) and does not rely on the usual kernel mechanisms.
Yes I see that you check/populate tlb for non KVM_GUEST_KSEG0 access,
for kvm_mips_translate_guest_kseg0_to_hpa() you do not, but now I notice
that you are not using the address directly but uses CKSEG0ADDR() on it,
which, as far as I can tell, gives you kernel mapping for the page,
correct? Why this is better than using get_user()? To save tlb entries?
--
Gleb.
next prev parent reply other threads:[~2013-02-15 18:42 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-22 2:33 [PATCH v2 00/18] KVM for MIPS32 Processors Sanjay Lal
2012-11-22 2:33 ` [PATCH v2 01/18] KVM/MIPS32: Infrastructure/build files Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 02/18] KVM/MIPS32: Arch specific KVM data structures Sanjay Lal
2012-12-26 13:14 ` Gleb Natapov
2013-01-24 13:22 ` Ralf Baechle
2013-01-31 20:12 ` David Daney
2013-02-06 13:11 ` Gleb Natapov
2012-11-22 2:34 ` [PATCH v2 03/18] KVM/MIPS32: Entry point for trampolining to the guest and trap handlers Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 04/18] KVM/MIPS32: MIPS arch specific APIs for KVM Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 05/18] KVM/MIPS32: KVM Guest kernel support Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 06/18] KVM/MIPS32: Privileged instruction/target branch emulation Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 07/18] KVM/MIPS32: MMU/TLB operations for the Guest Sanjay Lal
2013-02-06 12:08 ` Gleb Natapov
2013-02-15 18:19 ` Sanjay Lal
2013-02-15 18:41 ` Gleb Natapov [this message]
2013-02-16 15:57 ` Sanjay Lal
2013-02-16 16:21 ` Gleb Natapov
2012-11-22 2:34 ` [PATCH v2 08/18] KVM/MIPS32: Release notes and KVM module Makefile Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 09/18] KVM/MIPS32: COP0 accesses profiling Sanjay Lal
2012-11-22 11:45 ` Sergei Shtylyov
2013-02-06 13:17 ` Gleb Natapov
2013-02-15 18:22 ` Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 10/18] KVM/MIPS32: Guest interrupt delivery Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 11/18] KVM/MIPS32: Routines to handle specific traps/exceptions while executing the guest Sanjay Lal
2013-02-06 13:20 ` Gleb Natapov
2013-02-15 16:10 ` Sanjay Lal
2013-02-18 9:44 ` Gleb Natapov
2013-02-19 2:31 ` Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 12/18] MIPS: Export routines needed by the KVM module Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 13/18] MIPS: If KVM is enabled then use the KVM specific routine to flush the TLBs on a ASID wrap Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 14/18] MIPS: ASM offsets for VCPU arch specific fields Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 15/18] MIPS: Pull in MIPS fix: fix endless loop when processing signals for kernel tasks Sanjay Lal
2013-01-24 13:07 ` Ralf Baechle
2012-11-22 2:34 ` [PATCH v2 16/18] MIPS: Export symbols used by KVM/MIPS module Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 17/18] KVM/MIPS32: Do not call vcpu_load when injecting interrupts Sanjay Lal
2012-11-22 2:34 ` [PATCH v2 18/18] KVM/MIPS32: Binary patching of select privileged instructions Sanjay Lal
2012-11-26 18:53 ` [PATCH v2 00/18] KVM for MIPS32 Processors David Daney
2012-11-27 19:35 ` Sanjay Lal
2013-01-24 15:05 ` Ralf Baechle
2013-01-24 15:59 ` Sanjay Lal
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