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Date: Thu, 1 Apr 2021 16:41:42 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v4 15/46] KVM: PPC: Book3S 64: Move hcall early register
 setup to KVM
Message-ID: <YGVdFrsEtD88oB90@thinks.paulus.ozlabs.org>
References: <20210323010305.1045293-1-npiggin@gmail.com>
 <20210323010305.1045293-16-npiggin@gmail.com>
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On Tue, Mar 23, 2021 at 11:02:34AM +1000, Nicholas Piggin wrote:
> System calls / hcalls have a different calling convention than
> other interrupts, so there is code in the KVMTEST to massage these
> into the same form as other interrupt handlers.
> 
> Move this work into the KVM hcall handler. This means teaching KVM
> a little more about the low level interrupt handler setup, PACA save
> areas, etc., although that's not obviously worse than the current
> approach of coming up with an entirely different interrupt register
> / save convention.

[snip]

> @@ -1964,29 +1948,8 @@ EXC_VIRT_END(system_call, 0x4c00, 0x100)
>  
>  #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
>  TRAMP_REAL_BEGIN(system_call_kvm)
> -	/*
> -	 * This is a hcall, so register convention is as above, with these
> -	 * differences:

I haven't checked all the code changes in detail yet, but this comment
at least is slightly misleading, since under PR KVM, system calls (to
the guest kernel) and hypercalls both come through this path.

Paul.