Re: [PATCH v2 2/7] KVM: arm64: Add FEAT_TLBIRANGE support

From: Oliver Upton <oliver.upton@linux.dev>
To: Raghavendra Rao Ananta <rananta@google.com>
Cc: Oliver Upton <oupton@google.com>, Marc Zyngier <maz@kernel.org>,
	Ricardo Koller <ricarkol@google.com>,
	Reiji Watanabe <reijiw@google.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Will Deacon <will@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jing Zhang <jingzhangos@google.com>,
	Colton Lewis <coltonlewis@google.com>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v2 2/7] KVM: arm64: Add FEAT_TLBIRANGE support
Date: Tue, 4 Apr 2023 18:50:58 +0000	[thread overview]
Message-ID: <ZCxxklWzAz9K+aOP@linux.dev> (raw)
In-Reply-To: <ZCxvXq0dftq/Szra@linux.dev>

On Tue, Apr 04, 2023 at 06:41:34PM +0000, Oliver Upton wrote:
> On Mon, Apr 03, 2023 at 10:26:01AM -0700, Raghavendra Rao Ananta wrote:
> > On Wed, Mar 29, 2023 at 6:19 PM Oliver Upton <oliver.upton@linux.dev> wrote:
> > > > +     start = round_down(start, stride);                                      \
> > > > +     end = round_up(end, stride);                                            \
> > > > +     pages = (end - start) >> PAGE_SHIFT;                                    \
> > > > +                                                                             \
> > > > +     if ((!system_supports_tlb_range() &&                                    \
> > > > +          (end - start) >= (MAX_TLBI_OPS * stride)) ||                       \
> > >
> > > Doesn't checking for TLBIRANGE above eliminate the need to test against
> > > MAX_TLBI_OPS?
> > >
> > Derived from __flush_tlb_range(), I think the condition is used to
> > just flush everything if the range is too large to iterate and flush
> > when the system doesn't support TLBIRANGE. Probably to prevent
> > soft-lockups?
> 
> Right, but you test above for system_supports_tlb_range(), meaning that
> you'd unconditionally call __kvm_tlb_flush_vmid() below.

Gah, I misread the parenthesis and managed to miss your statement in the
changelog about !TLBIRANGE systems. Apologies.

-- 
Thanks,
Oliver