Re: [PATCH v2 01/12] arm/arm64: KVM: Formalise end of direct linear map

From: Steve Capper <Steve.Capper@arm.com>
To: Marc Zyngier <Marc.Zyngier@arm.com>
Cc: "crecklin@redhat.com" <crecklin@redhat.com>,
	"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	"bhsharma@redhat.com" <bhsharma@redhat.com>,
	Will Deacon <Will.Deacon@arm.com>, nd <nd@arm.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 01/12] arm/arm64: KVM: Formalise end of direct linear map
Date: Wed, 29 May 2019 09:26:26 +0000	[thread overview]
Message-ID: <20190529092616.GA7196@capper-debian.cambridge.arm.com> (raw)
In-Reply-To: <20190528170116.GA13287@capper-debian.cambridge.arm.com>

On Tue, May 28, 2019 at 05:01:29PM +0000, Steve Capper wrote:
> On Tue, May 28, 2019 at 05:27:17PM +0100, Marc Zyngier wrote:
> > Hi Steve,
> 
> Hi Marc,
> 
> > 
> > On 28/05/2019 17:10, Steve Capper wrote:
> > > We assume that the direct linear map ends at ~0 in the KVM HYP map
> > 
> > Do we? This has stopped being the case since ed57cac83e05f ("arm64: KVM:
> > Introduce EL2 VA randomisation").
> > 
> > > intersection checking code. This assumption will become invalid later on
> > > for arm64 when the address space of the kernel is re-arranged.
> > > 
> > > This patch introduces a new constant PAGE_OFFSET_END for both arm and
> > > arm64 and defines it to be ~0UL
> > > 
> > > Signed-off-by: Steve Capper <steve.capper@arm.com>
> > > ---
> > >  arch/arm/include/asm/memory.h   | 1 +
> > >  arch/arm64/include/asm/memory.h | 1 +
> > >  virt/kvm/arm/mmu.c              | 4 ++--
> > >  3 files changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> > > index ed8fd0d19a3e..45c211fd50da 100644
> > > --- a/arch/arm/include/asm/memory.h
> > > +++ b/arch/arm/include/asm/memory.h
> > > @@ -24,6 +24,7 @@
> > >  
> > >  /* PAGE_OFFSET - the virtual address of the start of the kernel image */
> > >  #define PAGE_OFFSET		UL(CONFIG_PAGE_OFFSET)
> > > +#define PAGE_OFFSET_END		(~0UL)
> > >  
> > >  #ifdef CONFIG_MMU
> > >  
> > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > > index 8ffcf5a512bb..9fd387a63b9b 100644
> > > --- a/arch/arm64/include/asm/memory.h
> > > +++ b/arch/arm64/include/asm/memory.h
> > > @@ -52,6 +52,7 @@
> > >  	(UL(1) << VA_BITS) + 1)
> > >  #define PAGE_OFFSET		(UL(0xffffffffffffffff) - \
> > >  	(UL(1) << (VA_BITS - 1)) + 1)
> > > +#define PAGE_OFFSET_END		(~0UL)
> > >  #define KIMAGE_VADDR		(MODULES_END)
> > >  #define BPF_JIT_REGION_START	(VA_START + KASAN_SHADOW_SIZE)
> > >  #define BPF_JIT_REGION_SIZE	(SZ_128M)
> > > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> > > index 74b6582eaa3c..e1a777275b37 100644
> > > --- a/virt/kvm/arm/mmu.c
> > > +++ b/virt/kvm/arm/mmu.c
> > > @@ -2202,10 +2202,10 @@ int kvm_mmu_init(void)
> > >  	kvm_debug("IDMAP page: %lx\n", hyp_idmap_start);
> > >  	kvm_debug("HYP VA range: %lx:%lx\n",
> > >  		  kern_hyp_va(PAGE_OFFSET),
> > > -		  kern_hyp_va((unsigned long)high_memory - 1));
> > > +		  kern_hyp_va(PAGE_OFFSET_END));
> > >  
> > >  	if (hyp_idmap_start >= kern_hyp_va(PAGE_OFFSET) &&
> > > -	    hyp_idmap_start <  kern_hyp_va((unsigned long)high_memory - 1) &&
> > > +	    hyp_idmap_start <  kern_hyp_va(PAGE_OFFSET_END) &&
> > >  	    hyp_idmap_start != (unsigned long)__hyp_idmap_text_start) {
> > >  		/*
> > >  		 * The idmap page is intersecting with the VA space,
> > > 
> > 
> > This definitely looks like a move in the wrong direction (reverting part
> > of the above commit). Is it that this is just an old patch that should
> > have been dropped? Or am I completely missing the point?
> 
> I suspect this is a case of me rebasing my series... poorly.
> I'll re-examine the logic here and either update the patch or the commit
> log to make it clearer.
>

Hi Marc,
Thanks, this was indeed an overzealous rebase. I've removed this patch from the
series and kvmtool is happy booting guests (when rebased to v5.2-rc2).

Cheers,
-- 
Steve

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