Re: [PATCH] x86/hyperv: Fix the detection of E820_TYPE_PRAM in a Gen2 VM

[Saurabh Singh Sengar]

On Thu, Aug 10, 2023 at 10:31:37PM -0700, Dexuan Cui wrote:
> A Gen2 VM doesn't support legacy PCI/PCIe, so both raw_pci_ops and
> raw_pci_ext_ops are NULL, and pci_subsys_init() -> pcibios_init()
> doesn't call pcibios_resource_survey() -> e820__reserve_resources_late();
> as a result, any emulated persistent memory of E820_TYPE_PRAM (12) via
> the kernel parameter memmap=nn[KMG]!ss is not added into iomem_resource
> and hence can't be detected by register_e820_pmem().
> 
> Fix this by directly calling e820__reserve_resources_late() in
> hv_pci_init(), which is called from arch_initcall(pci_arch_init).
> 
> It's ok to move a Gen2 VM's e820__reserve_resources_late() from
> subsys_initcall(pci_subsys_init) to arch_initcall(pci_arch_init) because
> the code in-between doesn't depend on the E820 resources.
> e820__reserve_resources_late() depends on e820__reserve_resources(),
> which has been called earlier from setup_arch().
> 
> For a Gen-2 VM, the new hv_pci_init() also adds any memory of
> E820_TYPE_PMEM (7) into iomem_resource, and acpi_nfit_register_region() ->
> acpi_nfit_insert_resource() -> region_intersects() returns
> REGION_INTERSECTS, so the memory of E820_TYPE_PMEM won't get added twice.
> 
> Changed the local variable "int gen2vm" to "bool gen2vm".
> 
> Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
>  arch/x86/hyperv/hv_init.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index b004370d3b01..6b22d49aee7b 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -13,6 +13,7 @@
>  #include <linux/io.h>
>  #include <asm/apic.h>
>  #include <asm/desc.h>
> +#include <asm/e820/api.h>
>  #include <asm/sev.h>
>  #include <asm/hypervisor.h>
>  #include <asm/hyperv-tlfs.h>
> @@ -282,15 +283,31 @@ static int hv_cpu_die(unsigned int cpu)
>  
>  static int __init hv_pci_init(void)
>  {
> -	int gen2vm = efi_enabled(EFI_BOOT);
> +	bool gen2vm = efi_enabled(EFI_BOOT);
>  
>  	/*
> -	 * For Generation-2 VM, we exit from pci_arch_init() by returning 0.
> -	 * The purpose is to suppress the harmless warning:
> +	 * A Generation-2 VM doesn't support legacy PCI/PCIe, so both
> +	 * raw_pci_ops and raw_pci_ext_ops are NULL, and pci_subsys_init() ->
> +	 * pcibios_init() doesn't call pcibios_resource_survey() ->
> +	 * e820__reserve_resources_late(); as a result, any emulated persistent
> +	 * memory of E820_TYPE_PRAM (12) via the kernel parameter
> +	 * memmap=nn[KMG]!ss is not added into iomem_resource and hence can't be
> +	 * detected by register_e820_pmem(). Fix this by directly calling
> +	 * e820__reserve_resources_late() here: e820__reserve_resources_late()
> +	 * depends on e820__reserve_resources(), which has been called earlier
> +	 * from setup_arch(). Note: e820__reserve_resources_late() also adds
> +	 * any memory of E820_TYPE_PMEM (7) into iomem_resource, and
> +	 * acpi_nfit_register_region() -> acpi_nfit_insert_resource() ->
> +	 * region_intersects() returns REGION_INTERSECTS, so the memory of
> +	 * E820_TYPE_PMEM won't get added twice.
> +	 *
> +	 * We return 0 here so that pci_arch_init() won't print the warning:
>  	 * "PCI: Fatal: No config space access function found"
>  	 */
> -	if (gen2vm)
> +	if (gen2vm) {
> +		e820__reserve_resources_late();
>  		return 0;
> +	}


Kind reminder to review this.

- Saurabh

>  
>  	/* For Generation-1 VM, we'll proceed in pci_arch_init().  */
>  	return 1;
> 
> -- 
> 2.25.1
>