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From: Andrew Scull <ascull@google.com>
To: Will Deacon <will@kernel.org>
Cc: kernel-team@android.com, Marc Zyngier <maz@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 02/21] KVM: arm64: Add stand-alone page-table walker infrastructure
Date: Thu, 10 Sep 2020 15:21:59 +0100	[thread overview]
Message-ID: <20200910142159.GF93664@google.com> (raw)
In-Reply-To: <20200910123712.GB18100@willie-the-truck>

On Thu, Sep 10, 2020 at 01:37:13PM +0100, Will Deacon wrote:
> On Wed, Sep 09, 2020 at 04:29:26PM +0100, Alexandru Elisei wrote:
> > On 9/7/20 4:23 PM, Will Deacon wrote:
> > > [..]
> > > +
> > > +int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > > +		     struct kvm_pgtable_walker *walker)
> > > +{
> > > +	struct kvm_pgtable_walk_data walk_data = {
> > > +		.pgt	= pgt,
> > > +		.addr	= ALIGN_DOWN(addr, PAGE_SIZE),
> > > +		.end	= PAGE_ALIGN(walk_data.addr + size),
> > > +		.walker	= walker,
> > > +	};
> > 
> > If the caller wants to walk [0x500, 0x1500), for PAGE_SIZE = 0x1000 (4K), the
> > function walks the range [0x0, 0x1000). Is that intentional?
> 
> Yes, although the caller specifies a base and a *size*, rather than an end
> address. As a concrete example, much of the hypervisor stage-1 mapping
> is created using PAGE_SIZE mappings of random ELF symbols, which correspond
> to arbitrary addresses. In these cases, we really do want to round-down the
> address and perform a PAGE_SIZE mapping.

I think Alexandru has a point here. Turning his example into something
equivalent that maps a random ELF symbol:

    struct some_hyp_state s = { ... };
    // &s == 0x500
    // sizeof(s) == PAGE_SIZE
    kvm_pgtable_walk(&s, sizeof(s), walker);

Given `s` straddles the two pages, the part in the second page won't be
mapped.

Should the end address instead be calculated as:

   .end = PAGE_ALIGN(addr + size),

> 
> The alternative would be to return an error if the size is not page-aligned,
> but I don't think that's really necessary, especially since we accept an
> unaligned base.
> 
> Will
> 
> -- 
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
> 
_______________________________________________
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Andrew Scull <ascull@google.com>
To: Will Deacon <will@kernel.org>
Cc: kernel-team@android.com, Gavin Shan <gshan@redhat.com>,
	Suzuki Poulose <suzuki.poulose@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Quentin Perret <qperret@google.com>,
	James Morse <james.morse@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 02/21] KVM: arm64: Add stand-alone page-table walker infrastructure
Date: Thu, 10 Sep 2020 15:21:59 +0100	[thread overview]
Message-ID: <20200910142159.GF93664@google.com> (raw)
In-Reply-To: <20200910123712.GB18100@willie-the-truck>

On Thu, Sep 10, 2020 at 01:37:13PM +0100, Will Deacon wrote:
> On Wed, Sep 09, 2020 at 04:29:26PM +0100, Alexandru Elisei wrote:
> > On 9/7/20 4:23 PM, Will Deacon wrote:
> > > [..]
> > > +
> > > +int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > > +		     struct kvm_pgtable_walker *walker)
> > > +{
> > > +	struct kvm_pgtable_walk_data walk_data = {
> > > +		.pgt	= pgt,
> > > +		.addr	= ALIGN_DOWN(addr, PAGE_SIZE),
> > > +		.end	= PAGE_ALIGN(walk_data.addr + size),
> > > +		.walker	= walker,
> > > +	};
> > 
> > If the caller wants to walk [0x500, 0x1500), for PAGE_SIZE = 0x1000 (4K), the
> > function walks the range [0x0, 0x1000). Is that intentional?
> 
> Yes, although the caller specifies a base and a *size*, rather than an end
> address. As a concrete example, much of the hypervisor stage-1 mapping
> is created using PAGE_SIZE mappings of random ELF symbols, which correspond
> to arbitrary addresses. In these cases, we really do want to round-down the
> address and perform a PAGE_SIZE mapping.

I think Alexandru has a point here. Turning his example into something
equivalent that maps a random ELF symbol:

    struct some_hyp_state s = { ... };
    // &s == 0x500
    // sizeof(s) == PAGE_SIZE
    kvm_pgtable_walk(&s, sizeof(s), walker);

Given `s` straddles the two pages, the part in the second page won't be
mapped.

Should the end address instead be calculated as:

   .end = PAGE_ALIGN(addr + size),

> 
> The alternative would be to return an error if the size is not page-aligned,
> but I don't think that's really necessary, especially since we accept an
> unaligned base.
> 
> Will
> 
> -- 
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
> 

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-09-10 14:22 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-07 15:23 [PATCH v4 00/21] KVM: arm64: Rewrite page-table code and fault handling Will Deacon
2020-09-07 15:23 ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 01/21] KVM: arm64: Remove kvm_mmu_free_memory_caches() Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 02/21] KVM: arm64: Add stand-alone page-table walker infrastructure Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08  0:03   ` Gavin Shan
2020-09-08  0:03     ` Gavin Shan
2020-09-10 10:57     ` Will Deacon
2020-09-10 10:57       ` Will Deacon
2020-09-09 15:29   ` Alexandru Elisei
2020-09-09 15:29     ` Alexandru Elisei
2020-09-10 12:37     ` Will Deacon
2020-09-10 12:37       ` Will Deacon
2020-09-10 14:21       ` Andrew Scull [this message]
2020-09-10 14:21         ` Andrew Scull
2020-09-11 10:15         ` Will Deacon
2020-09-11 10:15           ` Will Deacon
2020-09-11 11:22           ` Andrew Scull
2020-09-11 11:22             ` Andrew Scull
2020-09-07 15:23 ` [PATCH v4 03/21] KVM: arm64: Add support for creating kernel-agnostic stage-1 page tables Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08  1:09   ` Gavin Shan
2020-09-08  1:09     ` Gavin Shan
2020-09-07 15:23 ` [PATCH v4 04/21] KVM: arm64: Use generic allocator for hyp stage-1 page-tables Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08  1:03   ` Gavin Shan
2020-09-08  1:03     ` Gavin Shan
2020-09-07 15:23 ` [PATCH v4 05/21] KVM: arm64: Add support for creating kernel-agnostic stage-2 page tables Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 06/21] KVM: arm64: Add support for stage-2 map()/unmap() in generic page-table Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-10 11:20   ` Alexandru Elisei
2020-09-10 11:20     ` Alexandru Elisei
2020-09-10 12:34     ` Will Deacon
2020-09-10 12:34       ` Will Deacon
2020-09-10 13:55       ` Alexandru Elisei
2020-09-10 13:55         ` Alexandru Elisei
2020-09-07 15:23 ` [PATCH v4 07/21] KVM: arm64: Convert kvm_phys_addr_ioremap() to generic page-table API Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 08/21] KVM: arm64: Convert kvm_set_spte_hva() " Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 09/21] KVM: arm64: Convert unmap_stage2_range() " Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 10/21] KVM: arm64: Add support for stage-2 page-aging in generic page-table Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08 15:30   ` Alexandru Elisei
2020-09-08 15:30     ` Alexandru Elisei
2020-09-10 12:42     ` Will Deacon
2020-09-10 12:42       ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 11/21] KVM: arm64: Convert page-aging and access faults to generic page-table API Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08 15:39   ` Alexandru Elisei
2020-09-08 15:39     ` Alexandru Elisei
2020-09-07 15:23 ` [PATCH v4 12/21] KVM: arm64: Add support for stage-2 write-protect in generic page-table Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 13/21] KVM: arm64: Convert write-protect operation to generic page-table API Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 14/21] KVM: arm64: Add support for stage-2 cache flushing in generic page-table Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 15/21] KVM: arm64: Convert memslot cache-flushing code to generic page-table API Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 16/21] KVM: arm64: Add support for relaxing stage-2 perms in generic page-table code Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08 16:37   ` Alexandru Elisei
2020-09-08 16:37     ` Alexandru Elisei
2020-09-07 15:23 ` [PATCH v4 17/21] KVM: arm64: Convert user_mem_abort() to generic page-table API Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-09 14:20   ` Alexandru Elisei
2020-09-09 14:20     ` Alexandru Elisei
2020-09-09 17:12     ` Marc Zyngier
2020-09-09 17:12       ` Marc Zyngier
2020-09-10 10:51       ` Will Deacon
2020-09-10 10:51         ` Will Deacon
2020-09-10 10:58         ` Marc Zyngier
2020-09-10 10:58           ` Marc Zyngier
2020-09-10 13:10         ` Alexandru Elisei
2020-09-10 13:10           ` Alexandru Elisei
2020-09-10 13:20       ` Alexandru Elisei
2020-09-10 13:20         ` Alexandru Elisei
2020-09-07 15:23 ` [PATCH v4 18/21] KVM: arm64: Check the pgt instead of the pgd when modifying page-table Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 19/21] KVM: arm64: Remove unused page-table code Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-08 10:33   ` Marc Zyngier
2020-09-08 10:33     ` Marc Zyngier
2020-09-10 10:54     ` Will Deacon
2020-09-10 10:54       ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 20/21] KVM: arm64: Remove unused 'pgd' field from 'struct kvm_s2_mmu' Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-07 15:23 ` [PATCH v4 21/21] KVM: arm64: Don't constrain maximum IPA size based on host configuration Will Deacon
2020-09-07 15:23   ` Will Deacon
2020-09-09 14:53   ` Alexandru Elisei
2020-09-09 14:53     ` Alexandru Elisei
2020-09-07 17:16 ` [PATCH v4 00/21] KVM: arm64: Rewrite page-table code and fault handling Marc Zyngier
2020-09-07 17:16   ` Marc Zyngier
2020-09-07 17:31   ` Will Deacon
2020-09-07 17:31     ` Will Deacon
2020-09-10  4:06 ` Gavin Shan
2020-09-10  4:06   ` Gavin Shan
2020-09-10  4:11   ` Gavin Shan
2020-09-10  4:11     ` Gavin Shan
2020-09-10 10:58   ` Will Deacon
2020-09-10 10:58     ` Will Deacon

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