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Date:   Fri, 26 Aug 2022 09:53:29 +0200
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Subject: Re: [PATCH] Add support for ESRT loading under Xen
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To:     Demi Marie Obenour <demi@invisiblethingslab.com>
Cc:     linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        xen-devel@lists.xenproject.org, Ard Biesheuvel <ardb@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
References: <20220825215218.1606-1-demi@invisiblethingslab.com>
From:   Jan Beulich <jbeulich@suse.com>
In-Reply-To: <20220825215218.1606-1-demi@invisiblethingslab.com>
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On 25.08.2022 23:52, Demi Marie Obenour wrote:
> @@ -40,6 +41,38 @@
>  
>  #define efi_data(op)	(op.u.efi_runtime_call)
>  
> +static_assert(XEN_PAGE_SHIFT == EFI_PAGE_SHIFT,
> +              "Mismatch between EFI_PAGE_SHIFT and XEN_PAGE_SHIFT");
> +
> +bool xen_efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *md)
> +{
> +	struct xen_platform_op op = {
> +		.cmd = XENPF_firmware_info,
> +		.u.firmware_info = {
> +			.type = XEN_FW_EFI_INFO,
> +			.index = XEN_FW_EFI_MEM_INFO,
> +			.u.efi_info.mem.addr = phys_addr,
> +			.u.efi_info.mem.size = ((u64)-1ULL) - phys_addr,
> +		}
> +	};
> +	union xenpf_efi_info *info = &op.u.firmware_info.u.efi_info;
> +	int rc;
> +
> +	memset(md, 0, sizeof(*md)); /* initialize md even on failure */
> +	rc = HYPERVISOR_platform_op(&op);
> +	if (rc) {
> +		pr_warn("Could not obtain information on address %llu from Xen: "
> +			"error %d\n", phys_addr, rc);
> +		return false;
> +	}
> +
> +	md->attribute = info->mem.attr;
> +	md->type = info->mem.type;
> +	md->num_pages = info->mem.size >> XEN_PAGE_SHIFT;
> +	md->phys_addr = info->mem.addr;

As indicated in reply to your patch changing XEN_FW_EFI_MEM_INFO in
the hypervisor: While this may fit the ESRT purpose, the address you
return here is not necessarily the start of the region, and hence
this function is not a general Xen replacement for the non-Xen
function. Therefore I think it also shouldn't give the impression of
doing so.

Jan