linux-kernel - Re: [PATCH] Add support for ESRT loading under Xen

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Message-ID: <YwkKiFIKHG4IcCmH@itl-email>
Date:   Fri, 26 Aug 2022 14:01:44 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, Ard Biesheuvel <ardb@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH] Add support for ESRT loading under Xen

On Fri, Aug 26, 2022 at 09:53:29AM +0200, Jan Beulich wrote:
> 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.

Is this just a matter of renaming the function?  Is it possible to
implement the original function with the current hypervisor?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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