linux-kernel - Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags

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Message-ID: <aBD4RsUZp-BmcLwC@arm.com>
Date: Tue, 29 Apr 2025 17:03:18 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Ankit Agrawal <ankita@...dia.com>,
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Subject: Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using
 VMA flags

On Tue, Apr 29, 2025 at 11:14:37AM -0300, Jason Gunthorpe wrote:
> On Tue, Apr 29, 2025 at 02:27:02PM +0100, Catalin Marinas wrote:
> > BTW, we should reject exec mappings as well (they probably fail for S1
> > VFIO since set_pte_at() will try to do cache maintenance).
> 
> To be clear the S2 should leave the mapping as execute allowed
> though. Only the VM knows how it will use this memory and VM's do
> actually execute out of the cachable PFNMAP VMA today. The VM will set
> any execute deny/allow on its S1 table according to how it uses the
> memory.

If S2 is executable, wouldn't KVM try to invalidate the I-cache and it
won't have an alias to do this? Unless it doesn't end up in
stage2_map_walker_try_leaf() or the walk has been flagged as skipping
the CMO.

-- 
Catalin