linux-kernel - [RFC 01/48] mm/vmalloc: Introduce arch hooks to notify ioremap/unmap changes

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Date:   Wed, 19 Apr 2023 15:16:29 -0700
From:   Atish Patra <atishp@...osinc.com>
To:     linux-kernel@...r.kernel.org
Cc:     Rajnesh Kanwal <rkanwal@...osinc.com>,
        Atish Patra <atishp@...osinc.com>,
        Alexandre Ghiti <alex@...ti.fr>,
        Andrew Jones <ajones@...tanamicro.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Björn Töpel <bjorn@...osinc.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-coco@...ts.linux.dev, Dylan Reid <dylan@...osinc.com>,
        abrestic@...osinc.com, Samuel Ortiz <sameo@...osinc.com>,
        Christoph Hellwig <hch@...radead.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guo Ren <guoren@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
        Jiri Slaby <jirislaby@...nel.org>,
        kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        Mayuresh Chitale <mchitale@...tanamicro.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Uladzislau Rezki <urezki@...il.com>
Subject: [RFC 01/48] mm/vmalloc: Introduce arch hooks to notify ioremap/unmap changes

From: Rajnesh Kanwal <rkanwal@...osinc.com>

In virtualization, the guest may need notify the host about the ioremap
regions. This is a common usecase in confidential computing where the
host only provides MMIO emulation for the regions specified by the guest.

Add a pair if arch specific callbacks to track the ioremapped regions.

This patch is based on pkvm patches. A generic arch config can be added
similar to pkvm if this is going to be the final solution. The device
authorization/filtering approach is very different from this and we
may prefer that one as it provides more flexibility in terms of which
devices are allowed for the confidential guests.

Signed-off-by: Rajnesh Kanwal <rkanwal@...osinc.com>
Signed-off-by: Atish Patra <atishp@...osinc.com>
---
 mm/vmalloc.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index bef6cf2..023630e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -304,6 +304,14 @@ static int vmap_range_noflush(unsigned long addr, unsigned long end,
 	return err;
 }
 
+__weak void ioremap_phys_range_hook(phys_addr_t phys_addr, size_t size, pgprot_t prot)
+{
+}
+
+__weak void iounmap_phys_range_hook(phys_addr_t phys_addr, size_t size)
+{
+}
+
 int ioremap_page_range(unsigned long addr, unsigned long end,
 		phys_addr_t phys_addr, pgprot_t prot)
 {
@@ -315,6 +323,10 @@ int ioremap_page_range(unsigned long addr, unsigned long end,
 	if (!err)
 		kmsan_ioremap_page_range(addr, end, phys_addr, prot,
 					 ioremap_max_page_shift);
+
+	if (!err)
+		ioremap_phys_range_hook(phys_addr, end - addr, prot);
+
 	return err;
 }
 
@@ -2772,6 +2784,10 @@ void vunmap(const void *addr)
 				addr);
 		return;
 	}
+
+	if (vm->flags & VM_IOREMAP)
+		iounmap_phys_range_hook(vm->phys_addr, get_vm_area_size(vm));
+
 	kfree(vm);
 }
 EXPORT_SYMBOL(vunmap);
-- 
2.25.1