linux-kernel - Re: [PATCH] xen-pciback: Allow setting PCI_MSIX_FLAGS

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Date:   Mon, 14 Nov 2022 11:55:09 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        "moderated list:XEN HYPERVISOR INTERFACE" 
        <xen-devel@...ts.xenproject.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too

On 14.11.2022 11:31, Marek Marczykowski-Górecki wrote:
> When Xen domain configures MSI-X, the usual approach is to enable MSI-X
> together with masking all of them via the config space, then fill the
> table and only then clear PCI_MSIX_FLAGS_MASKALL. Allow doing this via
> QEMU running in a stub domain.
> 
> Previously, when changing PCI_MSIX_FLAGS_MASKALL was not allowed, the
> whole write was aborted, preventing change to the PCI_MSIX_FLAGS_ENABLE
> bit too.
> 
> Note the Xen hypervisor intercepts this write anyway, and may keep the
> PCI_MSIX_FLAGS_MASKALL bit set if it wishes to. It will store the
> guest-requested state and will apply it eventually.
> 
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>

Reviewed-by: Jan Beulich <jbeulich@...e.com>