KVM ARM Archive on lore.kernel.org
 help / color / Atom feed
From: Marc Zyngier <maz@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v2] KVM: arm64: Don't set HCR_EL2.TVM when S2FWB is supported
Date: Mon, 28 Oct 2019 16:19:55 +0000
Message-ID: <86pnigyh90.wl-maz@kernel.org> (raw)
In-Reply-To: <0c3291a7-18dc-1ae5-e706-8b04c9ab8a9e@arm.com>

On Mon, 28 Oct 2019 15:12:39 +0000,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> Hi,
> 
> Resending this email, because I replied only to the kvmarm list by accident,
> instead of replying to everyone involved.
> 
> On 10/28/19 1:05 PM, Christoffer Dall wrote:
> > On CPUs that support S2FWB (Armv8.4+), KVM configures the stage 2 page
> > tables to override the memory attributes of memory accesses, regardless
> > of the stage 1 page table configurations, and also when the stage 1 MMU
> > is turned off.  This results in all memory accesses to RAM being
> > cacheable, including during early boot of the guest.
> >
> > On CPUs without this feature, memory accesses were non-cacheable during
> > boot until the guest turned on the stage 1 MMU, and we had to detect
> > when the guest turned on the MMU, such that we could invalidate all cache
> > entries and ensure a consistent view of memory with the MMU turned on.
> > When the guest turned on the caches, we would call stage2_flush_vm()
> > from kvm_toggle_cache().
> >
> > However, stage2_flush_vm() walks all the stage 2 tables, and calls
> > __kvm_flush-dcache_pte, which on a system with S2FWD does ... absolutely
> > nothing.
> >
> > We can avoid that whole song and dance, and simply not set TVM when
> > creating a VM on a system that has S2FWB.
> >
> > Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
> > Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> > ---
> > I was only able to test this on the model with cache modeling enabled,
> > but even removing TVM from HCR_EL2 without having FWB also worked with
> > that setup, so the testing of this has been light.  It seems like it
> > should obviously work, but it would be good if someone with access to
> > appropriate hardware could give this a spin.
> >
> >  arch/arm64/include/asm/kvm_arm.h     |  3 +--
> >  arch/arm64/include/asm/kvm_emulate.h | 12 +++++++++++-
> >  2 files changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> > index ddf9d762ac62..6e5d839f42b5 100644
> > --- a/arch/arm64/include/asm/kvm_arm.h
> > +++ b/arch/arm64/include/asm/kvm_arm.h
> > @@ -61,7 +61,6 @@
> >   * RW:		64bit by default, can be overridden for 32bit VMs
> >   * TAC:		Trap ACTLR
> >   * TSC:		Trap SMC
> > - * TVM:		Trap VM ops (until M+C set in SCTLR_EL1)
> >   * TSW:		Trap cache operations by set/way
> >   * TWE:		Trap WFE
> >   * TWI:		Trap WFI
> > @@ -74,7 +73,7 @@
> >   * SWIO:	Turn set/way invalidates into set/way clean+invalidate
> >   */
> >  #define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \
> > -			 HCR_TVM | HCR_BSU_IS | HCR_FB | HCR_TAC | \
> > +			 HCR_BSU_IS | HCR_FB | HCR_TAC | \
> >  			 HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \
> >  			 HCR_FMO | HCR_IMO)
> >  #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF)
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index d69c1efc63e7..70509799a2a9 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -53,8 +53,18 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
> >  		/* trap error record accesses */
> >  		vcpu->arch.hcr_el2 |= HCR_TERR;
> >  	}
> > -	if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
> > +
> > +	if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) {
> >  		vcpu->arch.hcr_el2 |= HCR_FWB;
> > +	} else {
> > +		/*
> > +		 * For non-FWB CPUs, we trap VM ops (HCR_EL2.TVM) until M+C
> > +		 * get set in SCTLR_EL1 such that we can detect when the guest
> > +		 * MMU gets turned off and do the necessary cache maintenance
> > +		 * then.
> > +		 */
> > +		vcpu->arch.hcr_el2 &= ~HCR_TVM;
> 
> Don't we want to set the bit here, so we're consistent with the
> previous behaviour and the comment? Because with this patch, we
> never set HCR_EL2.TVM...

Of course you're right. This is how I plan to fix it:

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 47c774c2d18b..7b835337f78b 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -63,7 +63,7 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
 		 * MMU gets turned on and do the necessary cache maintenance
 		 * then.
 		 */
-		vcpu->arch.hcr_el2 &= ~HCR_TVM;
+		vcpu->arch.hcr_el2 |= HCR_TVM;
 	}
 
 	if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features))


Christoffer, please shout if you disagree.

	M.

-- 
Jazz is not dead, it just smells funny.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-28 13:05 Christoffer Dall
2019-10-28 13:28 ` Mark Rutland
2019-10-28 13:45 ` Marc Zyngier
2019-10-28 15:06 ` Alexandru Elisei
2019-10-28 15:12 ` Alexandru Elisei
2019-10-28 16:19   ` Marc Zyngier [this message]
2019-10-28 17:09     ` Mark Rutland
2019-11-06 13:02 ` Alexandru Elisei
2019-11-06 15:20   ` Christoffer Dall

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=86pnigyh90.wl-maz@kernel.org \
    --to=maz@kernel.org \
    --cc=alexandru.elisei@arm.com \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM ARM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvmarm/0 kvmarm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvmarm kvmarm/ https://lore.kernel.org/kvmarm \
		kvmarm@lists.cs.columbia.edu
	public-inbox-index kvmarm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/edu.columbia.cs.lists.kvmarm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git