From: Sean Christopherson <seanjc@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Marc Zyngier <maz@kernel.org>, Anup Patel <anup@brainfault.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Atish Patra <atishp@atishpatra.org>,
David Hildenbrand <david@redhat.com>, Tom Rix <trix@redhat.com>,
kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm-riscv@lists.infradead.org,
linux-riscv@lists.infradead.org, llvm@lists.linux.dev,
linux-kernel@vger.kernel.org,
Colton Lewis <coltonlewis@google.com>,
Peter Gonda <pgonda@google.com>,
Andrew Jones <andrew.jones@linux.dev>
Subject: Re: [PATCH v4 5/6] KVM: selftests: Make arm64's MMIO ucall multi-VM friendly
Date: Wed, 24 Aug 2022 15:32:07 +0000 [thread overview]
Message-ID: <YwZEdzHtWEfCpr7B@google.com> (raw)
In-Reply-To: <YwY9BYDUeiT87/Vs@google.com>
On Wed, Aug 24, 2022, Oliver Upton wrote:
> Hi Sean,
>
> On Wed, Aug 24, 2022 at 03:21:14AM +0000, Sean Christopherson wrote:
> > +/*
> > + * Sync a global pointer to the guest that has a per-VM value, in which case
> > + * writes to the host copy of the "global" must be serialized (in case a test
> > + * is being truly crazy and spawning multiple VMs concurrently).
> > + */
>
> Do we even care about writes to the host's copy of the global pointer?
> I don't see how the host pointer is used beyond serializing writes into
> a guest.
>
> IOW, it looks as though we could skip the whole global illusion
> altogether and write straight into guest memory.
*sigh*
This exact thought crossed my mind when I first looked at this code, but somehow
I couldn't come up with the obvious solution of using a temporary on-stack variable
to hold the desired value.
Something like this should work.
#define write_guest_global(vm, g, val) ({ \
typeof(g) *_p = addr_gva2hva(vm, (vm_vaddr_t)&(g)); \
typeof(g) _val = val; \
\
memcpy(_p, &(_val), sizeof(g)); \
})
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next prev parent reply other threads:[~2022-08-24 15:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-24 3:21 [PATCH v4 0/6] KVM: selftests: Implement ucall "pool" (for SEV) Sean Christopherson
2022-08-24 3:21 ` [PATCH v4 1/6] KVM: selftests: Consolidate common code for populating ucall struct Sean Christopherson
2022-08-24 3:21 ` [PATCH v4 2/6] KVM: selftests: Consolidate boilerplate code in get_ucall() Sean Christopherson
2022-08-24 3:21 ` [PATCH v4 3/6] KVM: selftests: Automatically do init_ucall() for non-barebones VMs Sean Christopherson
2022-08-24 3:21 ` [PATCH v4 4/6] tools: Add atomic_test_and_set_bit() Sean Christopherson
2022-08-24 3:21 ` [PATCH v4 5/6] KVM: selftests: Make arm64's MMIO ucall multi-VM friendly Sean Christopherson
2022-08-24 15:00 ` Oliver Upton
2022-08-24 15:32 ` Sean Christopherson [this message]
2022-08-24 3:21 ` [PATCH v4 6/6] KVM: selftests: Add ucall pool based implementation Sean Christopherson
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