linux-kernel - Re: [PATCH v6 05/11] arm64: rsi: Map unprotected MMIO as decrypted

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Message-ID: <Zwkl51C3DFEQQ0Jb@arm.com>
Date: Fri, 11 Oct 2024 14:19:35 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Gavin Shan <gshan@...hat.com>
Cc: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
	kvmarm@...ts.linux.dev, Suzuki K Poulose <suzuki.poulose@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	Alper Gun <alpergun@...gle.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v6 05/11] arm64: rsi: Map unprotected MMIO as decrypted

On Tue, Oct 08, 2024 at 10:31:06AM +1000, Gavin Shan wrote:
> On 10/5/24 12:43 AM, Steven Price wrote:
> > diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> > index d7bba4cee627..f1add76f89ce 100644
> > --- a/arch/arm64/kernel/rsi.c
> > +++ b/arch/arm64/kernel/rsi.c
> > @@ -6,6 +6,8 @@
> >   #include <linux/jump_label.h>
> >   #include <linux/memblock.h>
> >   #include <linux/psci.h>
> > +
> > +#include <asm/io.h>
> >   #include <asm/rsi.h>
> >   struct realm_config config;
> > @@ -92,6 +94,16 @@ bool arm64_is_protected_mmio(phys_addr_t base, size_t size)
> >   }
> >   EXPORT_SYMBOL(arm64_is_protected_mmio);
> > +static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
> > +{
> > +	if (arm64_is_protected_mmio(phys, size))
> > +		*prot = pgprot_encrypted(*prot);
> > +	else
> > +		*prot = pgprot_decrypted(*prot);
> > +
> > +	return 0;
> > +}
> > +
> 
> We probably need arm64_is_mmio_private() here, meaning arm64_is_protected_mmio() isn't
> sufficient to avoid invoking SMCCC call SMC_RSI_IPA_STATE_GET in a regular guest where
> realm capability isn't present.

I think we get away with this since the hook won't be registered in a
normal guest (done from arm64_rsi_init()). So the additional check in
arm64_is_mmio_private() is unnecessary.

-- 
Catalin