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Subject: Re: [RFC PATCH v2 08/19] RISC-V: KVM: Implement VCPU world-switch
To:     Anup Patel <Anup.Patel@wdc.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Radim K <rkrcmar@redhat.com>
Cc:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Atish Patra <Atish.Patra@wdc.com>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        Christoph Hellwig <hch@infradead.org>,
        Anup Patel <anup@brainfault.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20190802074620.115029-1-anup.patel@wdc.com>
 <20190802074620.115029-9-anup.patel@wdc.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Fri, 2 Aug 2019 10:30:10 +0200
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On 02/08/19 09:47, Anup Patel wrote:
> +	/* Save Host SSTATUS, HSTATUS, SCRATCH and STVEC */
> +	csrr	t0, CSR_SSTATUS
> +	REG_S	t0, (KVM_ARCH_HOST_SSTATUS)(a0)
> +	csrr	t1, CSR_HSTATUS
> +	REG_S	t1, (KVM_ARCH_HOST_HSTATUS)(a0)
> +	csrr	t2, CSR_SSCRATCH
> +	REG_S	t2, (KVM_ARCH_HOST_SSCRATCH)(a0)
> +	csrr	t3, CSR_STVEC
> +	REG_S	t3, (KVM_ARCH_HOST_STVEC)(a0)
> +

A possible optimization: if these cannot change while Linux runs (I am
thinking especially of STVEC and HSTATUS, but perhaps SSCRATCH can be
saved on kvm_arch_vcpu_load too) you can avoid the csrr and store.

Paolo