linux-kernel - Re: [PATCH v2 4/7] kvm/mips: rework guest entry logic

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Date:   Thu, 20 Jan 2022 18:29:25 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, aleksandar.qemu.devel@...il.com,
        alexandru.elisei@....com, anup.patel@....com,
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Subject: Re: [PATCH v2 4/7] kvm/mips: rework guest entry logic

On 1/20/22 18:15, Mark Rutland wrote:
> As above, we'll also need the guest_state_{enter,exit}() calls
> surrounding this (e.g. before that local_irq_enable() at the start of
> kvm_mips_handle_exit(),

Oh, indeed.  And there is also an interrupt-enabled area similar to 
s390's, in both vcpu_run and the exception handler entry point (which 
falls through to the exit handler created by kvm_mips_build_exit).  For 
example:

         /* Setup status register for running guest in UM */
         uasm_i_ori(&p, V1, V1, ST0_EXL | KSU_USER | ST0_IE);
         UASM_i_LA(&p, AT, ~(ST0_CU0 | ST0_MX | ST0_SX | ST0_UX));
         uasm_i_and(&p, V1, V1, AT);
         uasm_i_mtc0(&p, V1, C0_STATUS);
         uasm_i_ehb(&p);

I'd rather get rid altogether of the EQS for MIPS.

> and that needs to happen in noinstr code, etc.

There are bigger problems with instrumentation, because the 
runtime-generated code as far as I can tell is not noinstr.

Paolo