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From: Fuad Tabba <tabba@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org,
	"open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
	<kvmarm@lists.cs.columbia.edu>,
	"moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
	<linux-arm-kernel@lists.infradead.org>,
	Zenghui Yu <yuzenghui@huawei.com>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	kernel-team@android.com, stable@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: arm64: Commit pending PC adjustemnts before returning to userspace
Date: Tue, 11 May 2021 09:03:40 +0100	[thread overview]
Message-ID: <CA+EHjTzcfmt4mxh05a_P+nheQ_A2FuXhpgvKXuV5__pZP0SxkA@mail.gmail.com> (raw)
In-Reply-To: <20210510094915.1909484-3-maz@kernel.org>

Hi Marc,

> KVM: arm64: Commit pending PC adjustemnts before returning to userspace

s/adjustments/adjustments

On Mon, May 10, 2021 at 10:49 AM Marc Zyngier <maz@kernel.org> wrote:
>
> KVM currently updates PC (and the corresponding exception state)
> using a two phase approach: first by setting a set of flags,
> then by converting these flags into a state update when the vcpu
> is about to enter the guest.
>
> However, this creates a disconnect with userspace if the vcpu thread
> returns there with any exception/PC flag set. In this case, the exposed
> context is wrong, as userpsace doesn't have access to these flags
> (they aren't architectural). It also means that these flags are
> preserved across a reset, which isn't expected.
>
> To solve this problem, force an explicit synchronisation of the
> exception state on vcpu exit to userspace. As an optimisation
> for nVHE systems, only perform this when there is something pending.

I've tested this with a few nvhe and vhe tests that exercise both
__kvm_adjust_pc call paths (__kvm_vcpu_run and
kvm_arch_vcpu_ioctl_run), and the tests ran as expected.  I'll do the
same for v2 when you send it out.

Cheers,
/fuad

WARNING: multiple messages have this Message-ID (diff)
From: Fuad Tabba <tabba@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, kernel-team@android.com,
	stable@vger.kernel.org,
	"open list:KERNEL VIRTUAL MACHINE FOR ARM64 \(KVM/arm64\)"
	<kvmarm@lists.cs.columbia.edu>,
	"moderated list:ARM64 PORT \(AARCH64 ARCHITECTURE\)"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/2] KVM: arm64: Commit pending PC adjustemnts before returning to userspace
Date: Tue, 11 May 2021 09:03:40 +0100	[thread overview]
Message-ID: <CA+EHjTzcfmt4mxh05a_P+nheQ_A2FuXhpgvKXuV5__pZP0SxkA@mail.gmail.com> (raw)
In-Reply-To: <20210510094915.1909484-3-maz@kernel.org>

Hi Marc,

> KVM: arm64: Commit pending PC adjustemnts before returning to userspace

s/adjustments/adjustments

On Mon, May 10, 2021 at 10:49 AM Marc Zyngier <maz@kernel.org> wrote:
>
> KVM currently updates PC (and the corresponding exception state)
> using a two phase approach: first by setting a set of flags,
> then by converting these flags into a state update when the vcpu
> is about to enter the guest.
>
> However, this creates a disconnect with userspace if the vcpu thread
> returns there with any exception/PC flag set. In this case, the exposed
> context is wrong, as userpsace doesn't have access to these flags
> (they aren't architectural). It also means that these flags are
> preserved across a reset, which isn't expected.
>
> To solve this problem, force an explicit synchronisation of the
> exception state on vcpu exit to userspace. As an optimisation
> for nVHE systems, only perform this when there is something pending.

I've tested this with a few nvhe and vhe tests that exercise both
__kvm_adjust_pc call paths (__kvm_vcpu_run and
kvm_arch_vcpu_ioctl_run), and the tests ran as expected.  I'll do the
same for v2 when you send it out.

Cheers,
/fuad
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Fuad Tabba <tabba@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org,
	 "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)"
	<kvmarm@lists.cs.columbia.edu>,
	 "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)"
	<linux-arm-kernel@lists.infradead.org>,
	Zenghui Yu <yuzenghui@huawei.com>,
	 James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	 Alexandru Elisei <alexandru.elisei@arm.com>,
	kernel-team@android.com, stable@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: arm64: Commit pending PC adjustemnts before returning to userspace
Date: Tue, 11 May 2021 09:03:40 +0100	[thread overview]
Message-ID: <CA+EHjTzcfmt4mxh05a_P+nheQ_A2FuXhpgvKXuV5__pZP0SxkA@mail.gmail.com> (raw)
In-Reply-To: <20210510094915.1909484-3-maz@kernel.org>

Hi Marc,

> KVM: arm64: Commit pending PC adjustemnts before returning to userspace

s/adjustments/adjustments

On Mon, May 10, 2021 at 10:49 AM Marc Zyngier <maz@kernel.org> wrote:
>
> KVM currently updates PC (and the corresponding exception state)
> using a two phase approach: first by setting a set of flags,
> then by converting these flags into a state update when the vcpu
> is about to enter the guest.
>
> However, this creates a disconnect with userspace if the vcpu thread
> returns there with any exception/PC flag set. In this case, the exposed
> context is wrong, as userpsace doesn't have access to these flags
> (they aren't architectural). It also means that these flags are
> preserved across a reset, which isn't expected.
>
> To solve this problem, force an explicit synchronisation of the
> exception state on vcpu exit to userspace. As an optimisation
> for nVHE systems, only perform this when there is something pending.

I've tested this with a few nvhe and vhe tests that exercise both
__kvm_adjust_pc call paths (__kvm_vcpu_run and
kvm_arch_vcpu_ioctl_run), and the tests ran as expected.  I'll do the
same for v2 when you send it out.

Cheers,
/fuad

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-05-11  8:04 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10  9:49 [PATCH 0/2] KVM: arm64: Fixup PC updates on exit to userspace Marc Zyngier
2021-05-10  9:49 ` Marc Zyngier
2021-05-10  9:49 ` Marc Zyngier
2021-05-10  9:49 ` [PATCH 1/2] KVM: arm64: Move __adjust_pc out of line Marc Zyngier
2021-05-10  9:49   ` Marc Zyngier
2021-05-10  9:49   ` Marc Zyngier
2021-05-10 14:55   ` Alexandru Elisei
2021-05-10 14:55     ` Alexandru Elisei
2021-05-10 14:55     ` Alexandru Elisei
2021-05-10 15:08     ` Marc Zyngier
2021-05-10 15:08       ` Marc Zyngier
2021-05-10 15:08       ` Marc Zyngier
2021-05-10  9:49 ` [PATCH 2/2] KVM: arm64: Commit pending PC adjustemnts before returning to userspace Marc Zyngier
2021-05-10  9:49   ` Marc Zyngier
2021-05-10  9:49   ` Marc Zyngier
2021-05-10 14:55   ` Alexandru Elisei
2021-05-10 14:55     ` Alexandru Elisei
2021-05-10 14:55     ` Alexandru Elisei
2021-05-10 15:04     ` Marc Zyngier
2021-05-10 15:04       ` Marc Zyngier
2021-05-10 15:04       ` Marc Zyngier
2021-05-10 15:14       ` Alexandru Elisei
2021-05-10 15:14         ` Alexandru Elisei
2021-05-10 15:14         ` Alexandru Elisei
2021-05-11  7:44         ` Marc Zyngier
2021-05-11  7:44           ` Marc Zyngier
2021-05-11  7:44           ` Marc Zyngier
2021-05-11 16:50           ` Alexandru Elisei
2021-05-11 16:50             ` Alexandru Elisei
2021-05-11 16:50             ` Alexandru Elisei
2021-05-11  8:03   ` Fuad Tabba [this message]
2021-05-11  8:03     ` Fuad Tabba
2021-05-11  8:03     ` Fuad Tabba
2021-05-11  8:14     ` Marc Zyngier
2021-05-11  8:14       ` Marc Zyngier
2021-05-11  8:14       ` Marc Zyngier
2021-05-11  8:22       ` Fuad Tabba
2021-05-11  8:22         ` Fuad Tabba
2021-05-11  8:22         ` Fuad Tabba
2021-05-11  8:45         ` Marc Zyngier
2021-05-11  8:45           ` Marc Zyngier
2021-05-11  8:45           ` Marc Zyngier

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