linux-kernel - Re: Possible 5.19 regression for systems with 52-bit physical address support

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Date:   Thu, 28 Jul 2022 08:53:20 -0500
From:   Michael Roth <michael.roth@....com>
To:     <seanjc@...gle.com>
CC:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: Possible 5.19 regression for systems with 52-bit physical
 address support

On Thu, Jul 28, 2022 at 08:44:30AM -0500, Michael Roth wrote:
> Hi Sean,
> 
> With this patch applied, AMD processors that support 52-bit physical

Sorry, threading got messed up. This is in reference to:

https://lore.kernel.org/lkml/20220420002747.3287931-1-seanjc@google.com/#r

commit 8b9e74bfbf8c7020498a9ea600bd4c0f1915134d
Author: Sean Christopherson <seanjc@...gle.com>
Date:   Wed Apr 20 00:27:47 2022 +0000

    KVM: x86/mmu: Use enable_mmio_caching to track if MMIO caching is enabled

> address will result in MMIO caching being disabled. This ends up
> breaking SEV-ES and SNP, since they rely on the MMIO reserved bit to
> generate the appropriate NAE MMIO exit event.
> 
> This failure can also be reproduced on Milan by disabling mmio_caching
> via KVM module parameter.
> 
> In the case of AMD, guests use a separate physical address range that
> and so there are still reserved bits available to make use of the MMIO
> caching. This adjustment happens in svm_adjust_mmio_mask(), but since
> mmio_caching_enabled flag is 0, any attempts to update masks get
> ignored by kvm_mmu_set_mmio_spte_mask().
> 
> Would adding 'force' parameter to kvm_mmu_set_mmio_spte_mask() that
> svm_adjust_mmio_mask() can set to ignore enable_mmio_caching be
> reasonable fix, or should we take a different approach?
> 
> Thanks!
> 
> -Mike