From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org,
Lai Jiangshan <laijs@linux.alibaba.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH] KVM: X86: Don't reset dr6 unconditionally when the vcpu being scheduled out
Date: Tue, 10 Aug 2021 11:59:31 +0200 [thread overview]
Message-ID: <8726aff8-f7d0-d4e0-ed59-aeffc2a4c2f5@redhat.com> (raw)
In-Reply-To: <YRFdq8sNuXYpgemU@google.com>
On 09/08/21 18:54, Sean Christopherson wrote:
> Not directly related to this patch, but why does KVM_DEBUGREG_RELOAD exist?
> Commit ae561edeb421 ("KVM: x86: DR0-DR3 are not clear on reset") added it to
> ensure DR0-3 are fresh when they're modified through non-standard paths, but I
> don't see any reason why the new values_must_ be loaded into hardware. eff_db
> needs to be updated, but I don't see why hardware DRs need to be updated unless
> hardware breakpoints are active or DR exiting is disabled, and in those cases
> updating hardware is handled by KVM_DEBUGREG_WONT_EXIT and KVM_DEBUGREG_BP_ENABLED.
The original implementation of KVM_DEBUGREG_WONT_EXIT (by yours truly)
had a bug where it did not call kvm_update_dr7 and thus
KVM_DEBUGREG_BP_ENABLED was not set correctly. I agree that commit
70e4da7a8ff6 ("KVM: x86: fix root cause for missed hardware
breakpoints") should have gotten rid of KVM_DEBUGREG_RELOAD altogether.
Paolo
prev parent reply other threads:[~2021-08-10 9:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-08 23:29 [PATCH] KVM: X86: Don't reset dr6 unconditionally when the vcpu being scheduled out Lai Jiangshan
2021-08-09 16:54 ` Sean Christopherson
2021-08-09 17:43 ` [PATCH V2 1/3] KVM: X86: Remove unneeded KVM_DEBUGREG_RELOAD Lai Jiangshan
2021-08-09 17:43 ` [PATCH V2 2/3] KVM: X86: Set the hardware DR6 only when KVM_DEBUGREG_WONT_EXIT Lai Jiangshan
2021-08-10 10:07 ` Paolo Bonzini
2021-08-10 10:30 ` Lai Jiangshan
2021-08-10 10:35 ` Paolo Bonzini
2021-08-10 10:46 ` Lai Jiangshan
2021-08-10 12:49 ` Paolo Bonzini
2021-08-09 17:43 ` [PATCH V2 3/3] KVM: X86: Reset " Lai Jiangshan
2021-08-10 9:42 ` Paolo Bonzini
2021-08-10 10:14 ` Paolo Bonzini
2021-08-10 10:34 ` Lai Jiangshan
2021-08-10 10:41 ` Paolo Bonzini
2021-08-10 9:59 ` Paolo Bonzini [this message]
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