linux-kernel - RE: [PATCH 08/11] fbdev/hyperv: use pci aperture helpers

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Date:   Tue, 17 Jan 2023 18:42:51 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>
CC:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: RE: [PATCH 08/11] fbdev/hyperv: use pci aperture helpers

> From: Daniel Vetter <daniel.vetter@...ll.ch>
> Sent: Wednesday, January 11, 2023 7:41 AM
> [...]
> diff --git a/drivers/video/fbdev/hyperv_fb.c
> b/drivers/video/fbdev/hyperv_fb.c
> @@ -1076,9 +1076,7 @@ static int hvfb_getmem(struct hv_device *hdev,
> struct fb_info *info)
>         info->screen_size = dio_fb_size;
> 
>  getmem_done:
> -
> aperture_remove_conflicting_devices(info->apertures->ranges[0].base,
> -
> info->apertures->ranges[0].size,
> -                                           false,
> KBUILD_MODNAME);
> +       aperture_remove_conflicting_pci_devices(pdev,
> KBUILD_MODNAME);

NACK. I think the patch breaks Gen-2 VMs, because 'pdev' is NULL in a
Gen-2 VM.

A VM running on Hyper-V can be Gen-1 or Gen-2: see
https://learn.microsoft.com/en-us/windows-server/virtualization/hyper-v/plan/should-i-create-a-generation-1-or-2-virtual-machine-in-hyper-v

A Gen-2 VM doesn't have the legacy PCI Bus, and doesn't have a legacy
PCI VGA adapter device, so the 'pdev' is NULL here.

> 
>         if (gen2vm) {
>                 /* framebuffer is reallocated, clear screen_info to avoid
> misuse from kexec */